JP2624731B2 - Air-fuel ratio detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio detection device for an internal combustion engine, and more particularly to an air-fuel ratio detection device that detects a limit current.

[Conventional technology]

A conventional air-fuel ratio detection device determines whether control is performed with a lean air-fuel ratio or λ = 1 according to the operating state of an engine, as described in Japanese Patent Application Laid-Open No. 58-48749. The drive was switched to limit current detection and electromotive force detection. However, no consideration was given to the control method immediately after the engine was started.

[Problems to be solved by the invention]

In the above prior art, the disadvantage of the lean sensor capable of measuring the stoichiometric air-fuel ratio and the lean air-fuel ratio, that is, the detection accuracy near λ = 1 is poor, the detection is switched to the electromotive force measurement type in which the step changes at λ = 1. In order to improve the accuracy, in the fuel lean air-fuel ratio range, the drive circuit that measures the limit current using the oxygen pump action of zirconia is activated,
In the vicinity of the stoichiometric air-fuel ratio point, the driving circuit for measuring the electromotive force of the concentration cell is switched to detect the air-fuel ratio.

The object of the present invention is a drawback of the linear air-fuel ratio sensor,
In other words, the oxygen pumping current is 650 ° C to 700 ° C
Therefore, it is possible to improve that the detection accuracy is remarkably reduced until the engine is warmed up after the engine is started.

[Means for solving the problem]

The above object, a reference electrode and a detection electrode and a solid electrolyte, a detection element provided with a member that controls the gas diffusion in the detection electrode,
A heater for heating the detection element and a drive circuit thereof, and a circuit for measuring the electromotive force of the concentration cell of the detection element, and detecting a limit current of the detection element to change a gas component from fuel rich to fuel lean. An air-fuel ratio detection device for an internal combustion engine for measuring a mixture ratio of air and fuel of a fuel gas, comprising: a driving circuit portion for measuring the air-fuel ratio of the fuel gas after starting the air-fuel ratio detection device. After the start of the air-fuel ratio detection device, the detection element measures the air-fuel ratio with the electromotive force of the concentration cell for a period determined based on the temperature rise characteristics of the detection element, and after the elapse of the period, the limit battery is used. Means for switching to measure the air-fuel ratio,
It is achieved by having.

[Action]

Therefore, the electromotive force is measured until the detection element is heated to 650 ° C. to 700 ° C. after the start-up warm-up, and then the limit current is measured, so that the detection accuracy at the start-up warm-up can be improved.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First
FIG. 1 is a block diagram of an air-fuel ratio detection device related to air-fuel ratio control of an internal combustion engine according to the present invention. The air-fuel ratio sensor 1 includes a detection electrode 11, a reference electrode 12, an exhaust gas introduction hole 13, an atmosphere introduction chamber 14, and a heater unit 15.
The temperature is adjusted by the heater drive circuit unit 3. The air-fuel ratio detection device starts operating simultaneously with the start of the internal combustion engine, and energization of the heater is turned on to heat the sensor. Sensor 1
Is initially connected to the stoichiometric air-fuel ratio detection circuit 4, detects the electromotive force signal of the oxygen concentration cell, and outputs its output V _S to the air-fuel ratio
Give to. When the sensor 1 is sufficiently heated and it becomes possible to accurately measure the air-fuel ratio by pumping oxygen ions, the signal is sent to the switching switch 6, and from the electromotive force detection to the linear air-fuel ratio detection circuit 5 for oxygen ion current detection. The connection of the sensor 1 is switched. At the same time, a switch signal is given from the sensor temperature detection circuit unit to the air-fuel ratio control device 10, and a linear output signal
It switched to V _0, and to perform the air-fuel ratio control by the V ₀ thereafter. As the switching timing, a timing at which the temperature of the sensor reaches the set value and the temperature control starts can be selected. In other words, the heater was initially energized, but the current reached the set value and the energization was stopped.
Since the FF is repeated and the temperature is adjusted, the first energization OFF signal can be used.

FIG. 2 is a block diagram in the case where the stoichiometric air-fuel ratio detection circuit unit 4 and the linear air-fuel ratio detection circuit unit 5 are switched by the timer circuit unit 7. In this case, the time until switching is strictly different depending on the temperature of the internal combustion engine cooling water at the time of starting, etc., but the time required for warming up the sensor from the most cooled state can be used.

Fig. 3 shows the temperature rise characteristics of the sensor. The time to reach the temperature of about 350 ° C, at which the electromotive force can be measured and the stoichiometric air-fuel ratio can be detected, is t _s (second). The linear air-fuel ratio is detected by oxygen ion pumping. The time to reach about 700 ° C. is t ₀ (sec). Experiments have confirmed that t _s is usually around 10 seconds and t ₀ is as long as 30 to 60 seconds. Therefore,
By switching the air-fuel ratio detection according to an embodiment of FIG. 1 or FIG. 2, immediately after starting of a conventional on-- shortening the period can not be air-fuel ratio detected by using as an off-type O ₂ sensor is volume accuracy Air-fuel ratio control became possible.

Figure 4 is shows the output characteristics of the electromotive force V _s, fifth
The figure shows the output (V ₀ ) of the linear air-fuel ratio detection circuit. Pump current I _P is negative, at the stoichiometric air-fuel ratio point becomes positive in the lean side Ritsuchi side is I _P = 0.

〔The invention's effect〕

According to the present invention, it is possible to cover an increase in the activation time, which is a drawback of the linear air-fuel ratio detection sensor utilizing the oxygen ion pumping phenomenon, so that highly accurate and efficient air-fuel ratio control can be performed.

[Brief description of the drawings]

1 and 2 are block diagrams of an embodiment of the present invention, and FIG.
FIG. 4 shows an example of temperature rise data at the time of sensor heating, FIG. 4 shows air-fuel ratio-output characteristics by a stoichiometric air-fuel ratio detection circuit, and FIG. 5 shows air-fuel ratio-output characteristics by a linear air-fuel ratio detection circuit. 1 ... air-fuel ratio sensor, 2 ... sensor temperature detection circuit section, 3
... Heater drive circuit, 4... Stoichiometric air-fuel ratio detection circuit
5: Linear air-fuel ratio detection circuit unit 6: Switching switch
7: Timer circuit, 10: Air-fuel ratio control device.

Continuing from the front page (72) Inventor Sadayoshi Ueno 2520 Takada, Katsuta-shi, Ibaraki Inside Sawa Plant, Hitachi, Ltd. (72) Inventor Toyoaki Nakagawa 2 Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. Takayuki Itsuji 3085, Nishikonai, Higashiishikawa, Katsuta-shi, Ibaraki 5 Within Hitachi Automotive Engineering Co., Ltd. (56) References JP-A-60-111953 (JP, A)

Claims (1)

(57) [Claims] 1. A detecting element provided with a reference electrode, a detecting electrode, a solid electrolyte, a member for controlling the gas diffusion in the detecting electrode, a heater for heating the detecting element, and a drive circuit thereof.
A circuit unit for measuring the electromotive force of the concentration cell of the detection element,
An air-fuel ratio detection device for an internal combustion engine, which detects a limit current of the detection element and measures a mixture ratio of air and fuel of combustion gas, comprising a drive circuit unit for measuring a gas component over the entire range from fuel rich to fuel lean. Means for instructing the drive circuit unit of the heater to drive after the start of the air-fuel ratio detection device, and a period in which the detection element is determined based on a temperature rise characteristic of the detection element after the start of the air-fuel ratio detection device. Means for measuring the air-fuel ratio using the electromotive force of the concentration cell, and switching to measure the air-fuel ratio using the limit current after the lapse of the period, using the air-fuel ratio detection device for an internal combustion engine.