JPS6214349Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a comprehensive air-fuel ratio detection device provided in the exhaust system of an internal combustion engine.

[Conventional technology and problems]

Carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) contained in internal combustion engine exhaust gas
There are various methods for removing harmful substances such as: One method is to install a catalytic converter consisting of an oxidation catalyst, a reduction catalyst, or a three-way catalyst with both functions in the exhaust system of an internal combustion engine.
There are methods to purify harmful substances such as HC and NOx.
In this case, especially when a three-way catalyst is used, the catalyst is The purification efficiency of the converter is maximized.

Conventionally, an oxygen concentration detector is installed upstream of the catalytic converter in the exhaust system of an internal combustion engine, and secondary air is supplied into the exhaust system (secondary air supply method) or to the intake system based on the detection signal from this detector. The total air-fuel ratio is adjusted to the stoichiometric air-fuel ratio by adjusting the amount of fuel used and performing feedback control. (The oxygen concentration detector applies the principle of an oxygen concentration battery made of porcelain materials such as zirconia.) However, for example, when the engine load is large and the rotation speed increases, the exhaust gas temperature rises, making it difficult to detect the oxygen concentration. The detection element of the oxygen concentration detector becomes hot and thermally deteriorates, which causes a problem in that the detection accuracy of the oxygen concentration detector decreases and feedback control of the air-fuel ratio becomes difficult.

[Means for solving problems]

The comprehensive air-fuel ratio detection device according to the present invention includes an oxygen concentration detector installed in an exhaust pipe of an internal combustion engine, a means for detecting the temperature of a detection element of the oxygen concentration detector, and a means for detecting the temperature of a detection element of the oxygen concentration detector, and The oxygen concentration detector is characterized by comprising means for supplying secondary air for cooling to the oxygen concentration detector.

〔Example〕

This will be explained below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention, in which a catalytic converter (not shown) is provided in an exhaust pipe 2 of an exhaust system of an internal combustion engine 1. In FIG. An oxygen concentration detector 3 is installed upstream of this catalytic converter, and the detection signal of the detector 3 is basically calculated by a computer 4, and the air control valve 5 is
control. The air control valve 5 supplies secondary air supplied from the filter 6 via the air pump 7 linked to the internal combustion engine 1 to the exhaust port 1a of the internal combustion engine 1 from the air tube 9 via the check valve 8 for preventing backflow. When the oxygen concentration detector 3 detects that the overall air-fuel ratio is too rich, secondary air is supplied from the air tube 9, and conversely, when it detects that the overall air-fuel ratio is too lean, the secondary air amount is reduced to adjust the overall air-fuel ratio. Control to stoichiometric air-fuel ratio.

However, in such a device, the output voltage of the oxygen concentration detector may deviate to the lean side with respect to the actual total air-fuel ratio (solid line), as shown by the chain line in Figure 2, due to the phenomenon of unburned components adhering to the detector. In this case, even though the actual total air-fuel ratio is at the stoichiometric air-fuel ratio, the control system operates as if the total air-fuel ratio is on the rich side.

Therefore, a small tube 10 is provided to blow out a small amount of air (arrow a) toward the vicinity of the detection element of the oxygen concentration detector 3 (in the figure, it is inside the protective cover 3a and cannot be seen).
The small pipe 10 is connected to an air pump 7 via a control valve 11 operated by a computer 4. Therefore, the small amount of air blown out from the small tube 10 slightly dilutes the local air-fuel ratio of the atmosphere around the detection element with respect to the overall air-fuel ratio of the exhaust system, thereby offsetting the erroneous determination of excess concentration by the oxygen concentration detector 3 due to the unburned components mentioned above. urge Therefore, if this compensation air amount is controlled by the control valve 11 in proportion to the intake air amount and the total air-fuel ratio of the engine, the output voltage characteristic of the oxygen concentration detector 3 will change to the actual exhaust air-fuel ratio as shown by the solid line in FIG. Match. Furthermore, since the above-mentioned amount of compensation air is very small, the injection of this compensation air hardly changes the overall air-fuel ratio.

Furthermore, in order to efficiently achieve the effect of the above-mentioned compensation air injection with a small amount of air, for example, the outside of the cover 3a of the oxygen concentration detector 3 is covered with a shield 13 having holes, and the atmosphere compensation air (arrow a) is It is preferable that the gas reaches the sensing element without being significantly disturbed by the exhaust gas (arrow G). Also, small tube 10
The atmosphere compensation air may be constantly blown out through a throttling element without any particular control (no control valve 11 is provided), and this also substantially improves the characteristics of the oxygen concentration detector 3. can. Furthermore, atmosphere compensation air may be supplied from downstream of the air control valve 5.

In this embodiment, the small tube 10 also functions to supply secondary air for cooling to the oxygen concentration detector 3 when the detection element of the oxygen concentration detector 3 becomes hot. In this embodiment, the intake air amount obtained from the air flow meter 21 and the engine rotational speed obtained from the rotational speed sensor 22 are used to determine whether or not the detection element is at a high temperature. In other words, the value of (intake air amount/engine speed) is regarded as the engine load, and when the engine load and engine speed each reach a certain level or higher, that is, at high speed and high load, the sensing element will detect a high temperature. judge. Therefore, at high speed and high load, the computer 4 controls the small pipe 1 through the control valve 11.
Increase the amount of air from 0 to cool the sensing element.
Note that the temperature of the sensing element may be determined by detecting the exhaust gas temperature.

A second embodiment and a third embodiment of the present invention will be described with reference to FIGS. 3 and 4. In FIG. 3, the oxygen concentration detector 3 is fastened to the exhaust pipe 2 via the adapter 14 with a bolt 15. A hole 14a for attaching the small tube 10 to the adapter 14 is formed, and a seat 14b is formed on one surface of the adapter 14 by concentrically with the hole 14a, and a sleeve 16 having a plurality of holes is fixed thereto. The comprehensive air-fuel ratio detection device shown in FIG.
It can be fixed very easily by positioning and fastening with bolts 15. In Fig. 4, the protective cover 3a and the detection element 3b of the oxygen concentration detector 3 are shown.
To form an air flow path for atmosphere compensation between
Attach the small tube 10 to the detector body and drill a small hole 3d in the detector bracket 3c. The comprehensive air-fuel ratio detection device shown in FIG. 4 is integrated and is easy to handle, and the air for atmosphere compensation can be blown out very close to the detection element 3b, which is highly effective. It is necessary to modify the concentration detector.

Note that the present invention is applicable not only to systems that supply secondary air using an air pump but also to air suction systems.

[Effect of idea]

As described above, according to the present invention, the temperature of the sensing element of the oxygen concentration detector is always kept below a certain value, so thermal deterioration of the oxygen concentration detector is prevented, and feedback control of the total air-fuel ratio is always performed with high precision. The effect is that it becomes possible to

[Brief explanation of drawings]

Figure 1 is a schematic front view of one embodiment of the present invention;
The figure is an output diagram of the oxygen concentration detector, and FIGS. 3 and 4 are front views of other embodiments. 1...Internal combustion engine, 2...Exhaust pipe, 3...Oxygen concentration detector, 10...Small pipe.

Claims (1)

[Scope of utility model registration request] An oxygen concentration detector installed in an exhaust pipe of an internal combustion engine, a means for detecting the temperature of a detection element of the oxygen concentration detector, and a means for supplying cooling secondary air to the oxygen concentration detector when the detection element is at a high temperature. A comprehensive air-fuel ratio detection device comprising means for supplying.