JPH0772113A - Oxygen sensor controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To make it possible to prevent the generation of a low frequency oscillation concerning an oxygen sensor controller of an internal combustion engine. CONSTITUTION:A differential circuit 11 is supplied with an output voltage of an oxygen sensor 10 and output voltages of voltage generation circuits V1 and (r). A negative feedback circuit R feeds back an output of the differential circuit negatively to the differential circuit 11 to control current flowing through the oxygen sensor. A positive feedback circuit R2 feeds back an output signal of a low pass filter for removing a high pass component of the output of the differential circuit positively to the differential circuit 11. An impedance element R3 is provided in series or in parallel with the oxygen sensor 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor control device for an internal combustion engine, and more particularly to a limiting current type oxygen sensor control device used for detecting the air-fuel ratio of the internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, there is an oxygen sensor control device as described in JP-A-2-110858. In this conventional device, as shown in FIG. 2, one end of a limiting current type oxygen sensor 10 whose one end is connected to a power source V ₀ is connected to the inverting input terminal of an operational amplifier (opamp) 11 which is a differential circuit. the non-inverting input terminal of the operational amplifier 11 is connected via a resistor r to the power supply V _1, the power supply V ₁ is connected to a power supply V _0. The output terminal of the operational amplifier 11 is connected to the inverting input terminal via the resistor R ₁ as a negative feedback circuit, and the output of the operational amplifier 11 passes through the low-pass filter 12 and the terminal 15
Will be output. Further, the terminal 15 is connected to the non-inverting input terminal of the operational amplifier 11 via the resistor R ₂ as a positive feedback circuit.

The oxygen sensor 10 described above has a diffusion-controlling layer formed on the electrodes on the solid electrolyte body, and the saturation current (limit current) value between both electrodes is proportional to the air-fuel ratio. By negatively feeding back the output of the operational amplifier 11 via the resistor R ₁ , the operational amplifier 11 maintains the voltage between both electrodes of the oxygen sensor 10 at the set voltage, and then the oxygen sensor 10 is operated.
A current corresponding to the current flowing through (pump current) is taken out.

The power source V ₀ is offset so that the output current of the oxygen sensor 10 becomes positive. The power supply V ₁ corresponds to the electromotive force of the oxygen sensor 10, and the resistance r corresponds to the internal resistance of the sensor (only the real part of the impedance). The low-pass filter 12 cuts off the alternating current component of the output of the operational amplifier 11 to take out a current corresponding to the pump current, and the feedback resistor R ₂ causes a current corresponding to the pump current to flow through the resistor r, so that the non-inverting input terminal voltage of the operational amplifier 11 is changed. To raise. As a result, the voltage applied to the oxygen sensor 10 passes through the saturation region over the entire air-fuel ratio, and the measurement range of the limiting current is expanded.

[0005]

In the conventional device, the output of the low-pass filter 12 is positively fed back through the resistor R _2, and it is possible to prevent oscillation at a high frequency of, for example, 100 Hz or higher which can be cut off by the low-pass filter 12. , If the impedance of the oxygen sensor 10 is small, the pass band (1
Oscillation of low frequency (less than 00 Hz) cannot be prevented. Further, the oxygen sensor output is used for engine control, and since high responsiveness is desired, low frequency components cannot be easily removed.

The oxygen sensor currently used has a structure in which a solid electrolyte of zirconia oxide is sandwiched between platinum electrodes, and the impedance characteristic changes depending on the frequency f. As shown in FIG. Draw a circle,
At high frequencies, the impedance tends to be smaller than at low frequencies. Particularly in an oxygen sensor having a large polarization capacity, the impedance at a low frequency of about 10 Hz is much smaller than that at the time of direct current.

On the other hand, a heater is provided in the vicinity of the oxygen sensor for activating the sensor, and this heater is often turned on and off at a low frequency of about 10 Hz. Easily mixes with the oxygen sensor output. Therefore, the conventional device has a problem that low frequency oscillation may occur.

The present invention has been made in view of the above points,
It is an object of the present invention to provide an oxygen sensor control device for an internal combustion engine that prevents occurrence of low frequency oscillation by providing an impedance element in series or in parallel with the oxygen sensor.

[0009]

An oxygen sensor control apparatus for an internal combustion engine according to the present invention corresponds to a limiting current type oxygen sensor whose saturation current changes according to the air-fuel ratio of the internal combustion engine, and an electromotive force of the oxygen sensor. A voltage generating circuit that generates a predetermined voltage and outputs it through a resistance corresponding to the internal resistance of the oxygen sensor, and an output voltage of the oxygen sensor and an output voltage of the voltage generating circuit are applied to an inverting input terminal and a non-inverting input terminal, respectively. The supplied differential circuit, a negative feedback circuit that negatively feeds back the differential circuit output to the input terminal of the oxygen sensor output of the differential circuit to control the current flowing to the oxygen sensor, and the high range of the differential circuit output. It has a low-pass filter that removes components, and a positive feedback circuit that positively feeds back the output signal of the low-pass filter to the input terminal of the output of the voltage generation circuit of the differential circuit, and responds to the current flowing through the oxygen sensor. Electric current In the oxygen sensor control apparatus for an internal combustion engine that outputs from the low-pass filter, an impedance element provided in the oxygen sensor in series or in parallel, supplying oxygen sensor output through the impedance element to said differential circuit.

[0010]

In the present invention, the impedance element is provided in series or in parallel with the oxygen sensor so that the impedance of the oxygen sensor is apparently increased, and the circuit state is such that low frequency oscillation does not occur.

[0011]

FIG. 1 shows a circuit diagram of an embodiment of the device of the present invention. 2, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted.

In FIG. 1, an oxygen sensor 10 is fixed in an exhaust pipe of an internal combustion engine, and a pair of electrodes are formed on the inner and outer circumferences of a cylindrical solid electrolyte body made of stabilized zirconia or the like. , A diffusion-controlling layer is formed by sintering alumina, for example, on the outer peripheral electrodes. The diffusion-controlling layer is in contact with the exhaust gas in the exhaust pipe, and the saturation current value between the pair of electrodes is proportional to the air-fuel ratio of the exhaust gas. The operational amplifier 11 keeps a voltage between both electrodes of the oxygen sensor 10 at a set voltage and then takes out a current flowing through the oxygen sensor 10 and outputs it from a terminal 15 via a low-pass filter 12.

A resistor R ₃ as an impedance element is connected in series with the oxygen sensor 10 described above.
The other end of is connected to the inverting input terminal 11 of the operational amplifier 11 via this resistor R ₃ .

Here, the AC input signals of the non-inverting input terminal and the inverting input terminal of the operational amplifier 11 are V _IN and the operational amplifier 1
1 is the output signal of V _{3 and} the AC output signal of the terminal 15 is V _OUT ,
Set the impedance of the oxygen sensor 10 to Z (Z = a + b
i), the impedance including the resistance R ₃ in this impedance Z is Za (Za = R ₃ + Z), and the gain of the low-pass filter 12 is G.

[0015]

[Equation 1] Substituting equation (3) into equation (1),

[0016]

[Equation 2] When this equation is transformed,

[0017]

[Equation 3] Solving equation (4) for V _IN and substituting equation (3),

[0018]

[Equation 4] Since the oscillation condition is when the denominator on the right side of the above equation (5) is 0, oscillation can be prevented if this denominator is positive. Therefore,

[0019]

[Equation 5] As the resistor R _3, one having a value as small as possible is selected among those satisfying the expression (6). Further, the resistance value of the resistor r corresponding to the internal resistance of the oxygen sensor 10 corresponds to the internal resistance of the oxygen sensor 10 (the real part a of the impedance Z) and the resistance R ₃ corresponding to the impedance of the oxygen sensor 10 being compensated by the resistance R _{3. The} value is the sum of ₃ . In other words, from equation (6)

[0020]

[Equation 6] As a result, the apparent impedance of the oxygen sensor 10 is increased to a circuit state in which low frequency oscillation does not occur, and even if the temperature of the oxygen sensor 10 rises and the impedance Z decreases, the positive feedback results. Oscillation does not occur.

In the conventional device, a high-frequency AC voltage is superimposed on the power source V ₁ to control the impedance Z, which is proportional to the temperature of the oxygen sensor 10, to be constant. The above control can be incorporated as it is, and also in this case, low frequency oscillation can be prevented.

As the impedance element, another impedance element such as a capacitor or a coil may be used. In the case of a capacitor, the oxygen sensor 10 is provided in parallel to increase the apparent impedance of the oxygen sensor 10.

[0023]

As described above, according to the oxygen sensor control apparatus for an internal combustion engine of the present invention, by providing the impedance element in series with the oxygen sensor, the occurrence of low frequency oscillation can be prevented, which is extremely practical. It is useful.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a device of the present invention.

FIG. 2 is a circuit diagram of a conventional device.

FIG. 3 is a diagram showing impedance characteristics of an oxygen sensor.

[Explanation of symbols]

10 Oxygen Sensor 11 Operational Amplifier (Op Amp) 12 Low-pass Filter r Resistance R ₁ Negative Feedback Resistance R ₂ Positive Feedback Resistance R ₃ Resistance

Claims (1)

[Claims] 1. A limiting current type oxygen sensor whose saturation current changes according to the air-fuel ratio of an internal combustion engine, and a resistance corresponding to the internal resistance of the oxygen sensor, which generates a predetermined voltage corresponding to the electromotive force of the oxygen sensor. Voltage generation circuit that outputs through
A differential circuit in which the output voltage of the oxygen sensor and the output voltage of the voltage generation circuit are supplied to an inverting input terminal and a non-inverting input terminal, respectively, and the differential circuit output is an input terminal of the oxygen sensor output of the differential circuit. Negative feedback circuit that controls the current flowing through the oxygen sensor by negative feedback to the low-pass filter that removes the high-frequency component of the differential circuit output, and the output signal of the low-pass filter to generate the voltage of the differential circuit. A positive feedback circuit that positively feeds back to the input terminal of the circuit output, in an oxygen sensor control device of an internal combustion engine that outputs a current according to the current flowing through the oxygen sensor from the low-pass filter, in series with the oxygen sensor or An oxygen sensor control device for an internal combustion engine, wherein impedance elements are provided in parallel, and the oxygen sensor output through the impedance elements is supplied to the differential circuit.