JPH04221754A - Oxygen sensor with fin - Google Patents

Abstract

PURPOSE:To prevent heat deterioration of a seal member in a housing member by arranging a cooling fin on the outer surface of an outer cylinder by which a housing member is composed. CONSTITUTION:A detecting electrode 14 is located on the outer surface of a solid electrolytic cylinder body 12 the one end of which is closed and a reference electrode 16 is located on the inner surface thereof. An oxygen concentration detecting part 10 is formed and lead wires 28 and 32 are connected to the electrodes 14 and 16. A housing member 38 supports a detecting part 10, lead wires 28 and 32 are wrapped with the member 38, and a cooling fin 36 is arranged on the outer surface of an outer cylinder 34. A so constituted oxygen sensor 2 with a fin improves cooling efficiency through the action of the fin 36 and prevents heat deterioration of the seal member 30.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for an engine, and more particularly to an oxygen sensor having improved heat resistance by providing cooling fins.

0002

2. Description of the Related Art Many engine air-fuel ratio control systems have been proposed that control the air-fuel ratio based on the electromotive force output of an oxygen sensor attached to the exhaust gas line of the engine. The residual oxygen concentration in the exhaust gas is detected, and based on this, the mixture ratio of air and fuel supplied to the engine is adjusted. By combining this system with a three-way catalytic converter, CO, NOx, and HC contained in exhaust gas can be reduced.
It is possible to effectively remove harmful emissions such as

FIG. 4 is a partially cutaway side view of a conventional oxygen sensor 3 used in an air-fuel ratio control system. The oxygen concentration detection unit 10 includes a detection electrode 14 provided on the outer surface of a solid electrolyte cylinder 12 whose one end is closed, and a reference electrode 16 provided on the inner surface. The solid electrolyte cylinder 12 is made of, for example, yttria-stabilized zirconia (YSZ), and the electrodes 14 and 16 are made of, for example, platinum. A cylindrical heater 18 is inserted into the internal cavity of the solid electrolyte cylinder 12 . The oxygen concentration detection unit 10 is covered with a perforated protective cover 20, and the base of the protective cover 20 is fixed to the tip of a mounting bracket 22 for attachment to an exhaust gas line. Mounting bracket 22
A thread 23 is formed on the outer peripheral surface of the front end of the exhaust gas line, and the male thread 23 can be screwed into a female thread of a through hole provided in the wall of the exhaust gas line. The mounting bracket 22 has a central through hole on its axis, and the acidity concentration detection section 10 passing through this through hole is supported by the mounting bracket 22 via an insulating ceramic spacer 24. The front end of an inner cylinder 26 is connected to the base of the mounting bracket 22, and four hard lead wires 28 are passed through the inner cylinder 26.
passes. One end of two of these lead wires is electrically connected to the detection electrode 14 and the reference electrode 16 of the oxygen concentration detection unit 10, and one end of the other two lead wires is electrically connected to the heater 18. It is connected to the. These four hard lead wires 28 are connected to the sealing member 3 made of a rubber elastic body.
The flexible lead wires 32 are electrically connected to four flexible lead wires 32 inside the seal member 30 , and these flexible lead wires 32 are led out from the sealing member 30 . The seal member 30 is fitted into an outer cylinder 34, and the front end of the outer cylinder 34 is connected to the inner cylinder 26.
It is fitted onto the rear end of the The mounting bracket 22, the inner tube 26, and the outer tube 34 constitute a housing member 38 for supporting the oxygen concentration detection section 10 and wrapping the lead wires 28, 32. A sealing member 30 disposed within the housing member 38 prevents rainwater from entering the housing member 38.

When the oxygen sensor 3 is attached to the wall of the exhaust gas line using the mounting bracket 22, only the outer surface side of the solid electrolyte cylinder 12, that is, the detection electrode 14 side is exposed to the exhaust gas, and the solid electrolyte cylinder 12 is exposed to the exhaust gas. An electromotive force is generated between the sensing electrode 14 and the reference electrode 16 in accordance with the size of the difference in oxygen concentration between the inner and outer surfaces. At this time, the heater 18 is energized to set the operating temperature of the oxygen sensor 3.

[0005]

The oxygen sensor 3 attached to the exhaust gas line is exposed to high temperatures, and the temperature of the sealing member 30 becomes high as well as other parts. In the sealing member 30 whose temperature has risen abnormally, a portion of the rubber that is its material is thermally decomposed and generates gas. This thermal decomposition gas forms a film on the reference electrode 16 of the acidity concentration detecting section 10 and deteriorates the oxygen sensor 3. In other words, the electromotive force output for the same acidity concentration decreases. If the oxygen sensor 3 incorporated in the engine air-fuel ratio control system deteriorates in this way, the mixture ratio of air and fuel supplied to the engine will deviate from the appropriate air-fuel ratio control range, and the removal of harmful emissions from the exhaust gas will be interrupted. resulting in a significant decrease in the rate.

An object of the present invention is to improve the cooling efficiency of the housing member and prevent thermal deterioration of the seal member by providing cooling fins on the housing member.

[0007]

[Means for Solving the Problems] A finned oxygen sensor according to the present invention includes an oxygen concentration detecting section comprising a sensing electrode on the outer surface of a solid electrolyte cylinder whose one end is closed, and a reference electrode on the inner surface thereof; a plurality of lead wires each having one end connected to a sensing electrode and a reference electrode; a housing member that supports an oxygen concentration detection section and wraps around the lead wires and has cooling fins on its outer surface; and a housing member from which the plurality of lead wires are led out. and a sealing member for sealing the outlet port.

[0008]

[Function] The housing member provided with the cooling fins has a larger outer surface area, which increases cooling efficiency and prevents temperature rise. Therefore, the temperature rise of the seal member in this housing member is suppressed.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a partially cutaway side view of a finned oxygen sensor 2 according to an embodiment of the present invention. As shown in the figure, cooling fins 36 are provided on the outer surface of an outer cylinder 34 that constitutes a part of the housing member 38. By providing the cooling fins 36, the cooling efficiency of the housing member 38 is increased. Since the other configurations are similar to those shown in FIG. 4, detailed explanations will be omitted.

FIG. 2 is a schematic diagram of an engine air-fuel ratio control system that is an example of the use of the finned oxygen sensor 2. As shown in FIG. The combustible gas introduced through the fuel supply port 40 and the air introduced through the air supply port 42 are mixed into the mixer 44.
This mixed gas is supplied to the engine 48 via the throttle valve 46. A bypass 50 is formed between the air supply port 42 and the inlet of the throttle valve 46, and a control valve 52 is disposed in the middle of this bypass 50. The mixed gas combusted by the engine 48 passes through an exhaust gas line 54, is purified by a three-way catalytic converter 56, and is discharged. The finned oxygen sensor 2 according to this embodiment is attached to the exhaust gas line 54. The electromotive force output of this oxygen sensor 2 is input to the control unit 58, and the control unit 58 controls the control valve 52 based on this electromotive force output.
control opening and closing. That is, control is executed so that the mixture ratio of air and fuel supplied to the engine 48 becomes a predetermined value by feeding back the electromotive force generated by the oxygen sensor 2 corresponding to the residual oxygen concentration in the exhaust gas.

FIG. 3 shows the relationship between the oxygen-combustible gas equivalence ratio λ and the electromotive force of the oxygen sensor with a solid line, and the broken line shows the relationship between the equivalence ratio λ and the CO concentration and NOx concentration in the exhaust gas. It is a graph. λ=1 in the figure corresponds to a composition containing just the amount of air necessary for combustion of the combustible gas. This is called the stoichiometric air-fuel ratio, and when λ=1, C
Both the O concentration and the NOx concentration can be lowered at the same time. Dco is the allowable concentration of CO, Dno is the allowable concentration of NOx, and the diagonally shaded range (window) surrounded by the two dashed lines is the allowable range of the concentration of hazardous wastes.

Outer cylinder 34 that is part of housing member 38
Even the conventional oxygen sensor 2, which does not have cooling fins, initially exhibits the output characteristic of curve L1. The operating point P1 is within the permissible range of hazardous emissions concentrations. However, as the usage time becomes longer, the sealing member 30 undergoes thermal decomposition and deteriorates as described above, resulting in the characteristics shown by the curve L2. In the engine air-fuel ratio control system in which the oxygen sensor 3 is used, feedback control is performed so that the electromotive force output of this sensor is constant, so the operating point shifts to P2. In this way, the operating point of the oxygen sensor 3 deviates from the permissible range of harmful exhaust concentration. As a result, CO is emitted in excess of the permissible range.

However, in the finned oxygen sensor 2 according to this embodiment, the cooling efficiency is increased by the action of the cooling fins 36, and thermal deterioration of the seal member 30 is prevented. therefore,
The output characteristic represented by the curve L1 is maintained, and the operating point does not move from P1 within the permissible range of harmful exhaust concentration. In other words, a high harmful exhaust removal effect can be maintained. Note that in addition to the cooling fins 36, forced cooling means such as a fan may be provided.

[0015]

[Effects of the Invention] The finned oxygen sensor according to the present invention has
Since cooling fins are provided on the outer surface of the housing member to improve cooling efficiency, thermal deterioration of the seal member in the housing member can be prevented. Therefore, when using this sensor in an engine air-fuel ratio control system,
It is possible to stably output an electromotive force signal to maintain the concentration of harmful emissions in exhaust gas within an acceptable range even at high temperatures, making it possible to improve engine controllability and enable long-term operation.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway side view of a finned oxygen sensor according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an engine air-fuel ratio control system that is an example of using the finned oxygen sensor of FIG. 1;

FIG. 3 is a graph showing the relationship between the oxygen-combustible gas equivalence ratio λ and the electromotive force of the oxygen sensor, and the relationship between the equivalence ratio λ and the concentration of harmful emissions in exhaust gas.

FIG. 4 is a partially cutaway side view of a conventional oxygen sensor.

[Explanation of symbols]

2, 3...Oxygen sensor 10...Oxygen concentration detection section 12...Solid electrolyte cylinder 14...Detection electrode 16...Reference electrode 26...Inner cylinder 28...Hard lead wire 30...Seal member 32...Flexible lead wire 34...Outer cylinder 36...Cooling fin 38...Housing member

Claims (1)

[Claims] 1. An oxygen concentration detection unit comprising a solid electrolyte cylinder with one end closed, a detection electrode provided on the outer surface and a reference electrode provided on the inner surface, and a plurality of lead wires each having one end connected to each of the electrodes. a housing member that supports the oxygen concentration detection unit and wraps around the lead wires and has cooling fins on its outer surface; and a finned housing member that seals an outlet of the housing member from which the plurality of lead wires are led out. oxygen sensor.