KR900003857B1 - Air-fuel control device for internal combustion engine - Google Patents

Abstract

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Description

Air-fuel ratio control device

1 is a block diagram of an air-fuel ratio control apparatus for an internal combustion engine of this invention and a conventional apparatus.

2 is a flowchart showing an operation according to the present invention.

3 is a characteristic diagram of an air-fuel ratio sensor in the air-fuel ratio control apparatus of this invention and a conventional internal combustion engine.

4 is a characteristic diagram of the air-fuel ratio sensor of FIG.

5 is a flowchart showing the operation of the conventional air-fuel ratio control apparatus.

6 is a waveform diagram showing the operation of the conventional air-fuel ratio control device.

* Explanation of symbols for main parts of the drawings

1: internal combustion engine 2: intake pipe

3: pressure sensor 5: rotation sensor

6 injector 7 exhaust pipe

8: air-fuel ratio sensor 9: control device

10: water temperature sensor 81: oxygen pump container

82: oxygen cell container 93: microprocessor

94: ROM 95: RAM

100: resistor

The present invention relates to an air-fuel ratio control apparatus of an internal combustion engine that performs feedback control of an air-fuel ratio by using an air-fuel ratio sensor with a heater, and particularly, to protect the breakdown at low temperature of the air-fuel ratio sensor.

Conventionally, in an air-fuel ratio feedback control device using an air-fuel ratio sensor (oxygen sensor) in which the output voltage is inverted at a theoretical performance ratio, when the internal combustion engine is in a light load state or the air-fuel ratio sensor is mounted behind the exhaust pipe, the temperature of the air-fuel ratio sensor is low. In the case where it is not activated, it has been put to practical use to keep the sensor at a high temperature by incorporating an electric heater.

Some air-fuel ratio sensors that output analog values that change linearly with the air-fuel ratio have been put to practical use. However, the type air-fuel ratio sensor is also equipped with an electric heater for the purpose of improving or activating the output accuracy.

The air-fuel ratio feedback control using the air-fuel ratio sensor is widely used in internal combustion engines equipped with a carburetor or a fuel injection device because of exhaust gas purification. Here, a system using an air-fuel ratio sensor that generates a linear output with respect to an air-fuel ratio using a speed denslty type fuel injection device as a conventional example will be described. FIG. 1 shows the configuration of the air-fuel ratio control apparatus of the internal combustion engine of the present invention, which will be described below and conventionally, and will be described with reference to FIG. 1 when describing the air-fuel ratio control apparatus of the conventional internal combustion engine.

In FIG. 1, 1 is an internal combustion engine, 2 is an intake pipe connected to this internal combustion engine 1, and 3 is a throttle valve provided in this intake pipe 2. The pressure in the intake pipe 2 is detected by the pressure sensor 4, and the detected pressure is sent to the AD converter 91.

In addition, the signal of the temperature sensor 10 for detecting the temperature of the internal combustion engine 1 is also sent to the AD converter 91. The rotation of the internal combustion engine 1 is detected by the rotation sensor 5 as a pulse, and the output of the rotation sensor 5 is sent to the input circuit 91.

Further, fuel is injected into the intake pipe 2 by the injector 6, and the injector 6 is driven by the output of the output circuit 96. The exhaust pipe 7 is connected to the internal combustion engine 1, and the output corresponding to the air-fuel ratio in the exhaust gas component in the exhaust pipe 7 is sent from the air-fuel ratio sensor 8 to the AD converter 91.

On the other hand, 9 is a control device for generating the drive pulse width of the injector 6 by calculating the required fuel amount from information such as the pressure sensor 4, the rotation sensor 5, the air-fuel ratio sensor 8 and the like. In the controller 9, the AD converter 91 converts analog signals such as the air-fuel ratio sensor 8 and the pressure sensor 4 into digital values and sends them to the microprocessor 3.

The input circuit 92 is an input circuit for level converting the rotation sensor 5 and the pulse input signal, and this output is also sent to the microprocessor 93. The microprocessor 93 calculates the amount of fuel to be supplied to the internal combustion engine 1 based on the digital and pulse signals obtained from the AD converter 91 and the input circuit 92, and drives the driving pulse of the injector 6 according to the result. To print the width. The control procedure and data of the microprocessor 3 are stored in advance in the ROM 94, and the RAM 95 is configured to temporarily store data in the calculation process. The injector 6 is driven by the output circuit 96 in accordance with the output signal of the microprocessor 93.

The air-fuel ratio sensor 8 of the first part is constructed as shown in FIG. 3, 81 is an oxygen pump container, 82 is an oxygen cell container, 83a and 83b are porous electrodes, 84 is a diffusion chamber, and 85 is A reference voltage source, 86 is a comparative amplifier, 87 is a pump drive circuit, and 88 is a resistor for detecting a current of the pump. In addition, 103 is an electrical insulator, and a resistor 100 is formed on the electrical insulator 103. The resistor 100 serves as a heater and 102 is an air gap.

The configuration of the air-fuel ratio sensor 8 is already known (Japanese Patent Laid-Open No. 59-19046 and Japanese Patent Laid-Open No. 60-128349), and the reference voltage source 85 is set to about 0.4v. The voltage of the battery container 82 is compared in the comparison amplifier 86, and the exhaust gas in the diffusion chamber 84 is allowed to flow through the pump driving circuit 87 to flow the current through the pump driving circuit 87 so that the deviation becomes zero. It is equivalent to the air-fuel ratio.

Using this principle, both the lean side and the rich side of the theoretical air-fuel ratio can be detected, and the measurement result can be taken out as the voltage across the resistor 88, and as shown in FIG. A linear output voltage can be obtained for the range. The resistance value 100 is energized by the output circuit 97 in the control device 9 during engine operation and is activated by heating the air-fuel ratio sensor 8.

Next, a conventional control method of the air-fuel ratio feedback using the air-fuel ratio sensor 8 will be described with reference to FIG. 5 is a flowchart showing the control procedure of the control device 9 shown in FIG.

In step S ₁ , the pulse signal input from the rotation sensor 5, that is, the engine speed Ne, is read. In step S ₂ , the value Pb of the intake pipe pressure (absolute pressure) obtained from the pressure sensor 4 is read. In S ₃ , the basic drive pulse width γ ₀ of the injector 6 is calculated based on the information read in steps S ₁ and S ₂ .

The equation is expressed by γ ₀ = K · Pb · η _v , where K is an integer and η _v is a predetermined charging efficiency corresponding to the intake pressure Pb and the engine speed Ne. Although not shown in FIG. 5, the actual drive pulse width γ ₀ is increased and corrected at low temperatures by the signal of the water temperature sensor 10.

Next, it is a target air-fuel ratio (A / F) S set in step S _4. This target performance ratio (A / F) S is shown, for example, in FIG. 6 (FIG. 6 (a) shows an engine stop, an operation cycle, and FIG. 6 (b) shows an on / off cycle of a heater of an air-fuel ratio sensor). As described above, the optimum power performance and fuel ratio are set so as to correspond to the engine speed Ne and the intake pressure Ph, but may be changed again depending on the engine temperature or acceleration / deceleration state.

Step S ₅ in obtaining an output signal (A / F) R to read the deviation of the air-fuel ratio at the step S ₆ (A / F) S target air-fuel ratio (A / F) R of the air-fuel ratio sensor 8 suitable for the value of the gain ( Integrate to Gain).

Step S ₇ in the upper and lower integral values, which has a value of I pre-(Limit) value I (LMT) to exceed sure whether determined by the limit values within If at the step S ₈ the correction value I ₁ = I a, and if the limit value a of the If exceeded, the correction value I ₁ = I (LMT) is determined in step S ₉ . Next, the injection pulse width γ in step S ₁₀ is obtained by multiplying the correction value I ₁ by the basic injection pulse width γ ₀ first obtained in step S ₃ .

The above operation is repeated, and the air-fuel ratio is feedback controlled so as to reach the target value A / F. However, the above operation is that the air-fuel ratio sensor 8 should be activated by the exhaust gas temperature of the engine or the heating of the resistor 100.

In general, when the engine is lightly loaded, the exhaust temperature is low so that it is difficult to reach the activation temperature. Thus, an electric heater is incorporated in the air-fuel ratio sensor, and the engine is energized during operation of the engine as shown in FIG.

In the air-fuel ratio control apparatus of the conventional internal combustion engine as described above, the engine functions normally under normal ambient temperature, but in a low-temperature atmosphere such as 0 ° to -30 ° C, if the engine is stopped before engine preheating is completed after the engine is started, In addition, since the temperature of the exhaust pipe is not sufficiently raised, water vapor contained in the exhaust gas layer during operation may become water droplets in the exhaust pipe, and water droplets may also adhere to the air-fuel ratio sensor.

Since the air-fuel ratio sensor has a structure with air gaps or pores, when the water-gap is left at a low temperature with water droplets attached to the air gap, the water droplets are frozen and the container of the air-fuel ratio sensor is destroyed by expansion due to freezing.

The present invention has been invented to solve such a problem, and an object thereof is to obtain an air-fuel ratio control device capable of preventing destruction of the air-fuel ratio sensor due to freezing of water droplets even when water droplets are attached to the air-fuel ratio sensor.

The air-fuel ratio control apparatus of the present invention is provided with a temperature sensor for detecting the engine temperature, and means for energizing the heat transfer heater of the air-fuel ratio sensor even after the engine stops by discriminating the detected temperature of the temperature sensor.

In the present invention, the engine temperature is detected by the temperature sensor, and if the engine temperature is equal to or less than the predetermined value at the time of engine stop, the engine is heated by energizing the electric heater of the air-fuel ratio sensor for a predetermined time after engine stop.

Embodiments of the air-fuel ratio control apparatus of the present invention will be described with reference to the drawings. The configuration of the present invention is the same as that of FIG. 1 described above, but the calculation processing and data setting method in the computing unit centering on the microprocessor 93 in the control unit 9 is different from the conventional apparatus, and the flow of FIG. New features have been added to the chart.

In the flowchart of FIG. 2, in step 200, it is determined whether or not the engine is stopped by turning off the key switch, and after engine stop, the signal of the water temperature sensor 10 is read in step 201, whereby the coolant temperature is increased. It determines whether it is a predetermined value (for example, 70 degreeC or more), and if it is below a predetermined value, in step 202, the timer of heater electricity is operated.

While the timer is operating, power is supplied to the resistance value 100 of the air-fuel ratio sensor 8 through the output circuit 97, and the air-fuel ratio sensor 8 is heated.

The operation time of this timer is enough time to evaporate the moisture attached to the air-fuel ratio sensor 8, and it may be about several minutes when the ambient temperature is low.

According to the present invention, when the engine is stopped within a short time after the engine operation has not sufficiently risen after the engine starts, the engine operating temperature is determined by the engine coolant temperature. After stopping, electricity is supplied to the heater of the air-fuel ratio sensor only for a predetermined time, and the water or water droplets attached to the air-fuel ratio sensor evaporate. Thus, when the ambient temperature is low, the water attached to the air-fuel ratio sensor freezes with time and destroys the air-fuel ratio sensor. The problem can be completely prevented.

Claims (1)

An air-fuel ratio sensor mounted on the exhaust pipe and outputting air-fuel ratio information based on exhaust gas components, an electric heat heater integrated with the air-fuel ratio sensor, a temperature sensor for detecting engine temperature, and a stationary detecting means for detecting the engine's operation; A temperature discriminating means for determining that the engine temperature is lower than a predetermined value by the temperature sensor, a timer for operating only a predetermined time after the stopping detecting means is operated when the temperature detecting means is operating when the stopping detecting means is operated, And a means for energizing the heater during timer operation.

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