JPS62142263A - Detecting unit of air-fuel ratio measuring instrument - Google Patents

Abstract

PURPOSE:To prevent a particle from sticking to a weighing orifice by providing a heating means and heating an exhaust gas weighing orifice. CONSTITUTION:A detecting unit is constituted so that an exhaust gas is brought to sampling from an exhaust system, air is mixed in the sampling exhaust gas in a prescribed ratio, a mixed gas is oxidized completely and an unburned component is burned completely, and by detecting a residual oxigen concentration in the mixed gas, an analog signal corresponding to the air-fuel ratio of an air-fuel mixture for combustion is outputted to an air-fuel ratio arithmetic and display device. The mixed gas of a high temperature passing through an oxigen sensor 76 is led to the upstream end of paths 84, 86 for heating of a heat exchanger 78 through pipes 88, 90, collides with heat exchangers 80, 82 being in the vicinity of an exhaust gas and air weighing orifice 60 and 62, and heats these orifices and raises a temperature. Also, the remaining heat of a heater 70 heats the orifices 60, 62 through a metallic block 28. As a result, the floating particles of a sampling exhaust gas flow, etc. are deflected to the inside in the radial direction toward the center of a flow passing through the orifices 60, 62, and the sticking of the particles to the surface of the orifice is obstructed effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio measuring device for measuring the air-fuel ratio of a combustion mixture supplied to an internal combustion engine, and more specifically,
The present invention relates to a detection unit used in an air-fuel ratio measurement device to output an analog signal according to the air-fuel ratio of a combustion mixture.

[Prior art and problems]

In performance testing and diagnosis of internal combustion engines, it is necessary to measure the air-fuel ratio of the combustion air-fuel mixture supplied to the cylinders. In addition, the air-fuel ratio of the combustion mixture is detected, and the actual air-fuel ratio is set to a predetermined target air-fuel ratio (for example,
It is also well known to control a fuel supply system to achieve a stoichiometric air-fuel ratio.

Generally, the air-fuel ratio can be measured or detected by detecting residual oxygen in the exhaust gas using an oxygen sensor placed in the exhaust system. However, this method cannot be applied when the air-fuel ratio of the combustion mixture is richer than the stoichiometric air-fuel ratio and there is no residual oxygen in the exhaust gas.

For example, the measuring device disclosed in Japanese Unexamined Patent Publication No. 59-2-840 solves this drawback. In this air-fuel ratio measurement device, exhaust gas is sampled from the engine exhaust system, and new air taken in from the outside world is mixed with numbered exhaust gas at a predetermined ratio. amount of oxygen is added.The mixed gas of exhaust gas and air is then sent to the oxidation catalyst device, and the unburned components in the exhaust gas are completely burned.The mixed gas oxidized in this way is The residual oxygen concentration is detected by contacting the oxygen sensor.The air-fuel ratio of the combustion mixture can be determined by substituting the residual oxygen concentration thus detected into a predetermined calculation formula. Since oxygen is added to the gas, it is possible to measure the air-fuel ratio of a rich mixture that has an air-fuel ratio less than the stoichiometric air-fuel ratio.

As disclosed in Japanese Unexamined Patent Publication No. 59-2-840, a mixing mechanism with a metering orifice is used to mix the sampling exhaust gas and oxygen introduction air at a constant ratio. Since the flow rate of the fluid flowing through a total of one orifice depends on the inner diameter of the orifice, it is necessary to keep the inner diameter of the orifice constant at all times in order to keep the mixing ratio constant. The internal diameter of the orifice is extremely small, typically about II■. However, the sampled exhaust gas contains particles such as carbon, and this type of particle is (1
There was a problem in that the air adhered to the gas metering orifice, causing the inner diameter of the orifice to change during metering, which hindered accurate measurement of the air-fuel ratio.

[Purpose of the invention]

An object of the present invention is to prevent particles from adhering to the timing orifice and to enable accurate measurement of the air-fuel ratio.

Summary of Means and Effects for Solving Problem C] The present invention provides a detection unit used in an air-fuel ratio measuring device to output an analog signal according to the air-fuel ratio of the combustion mixture. be. This detection unit is (a)
(I7) an exhaust gas sampling pipe whose one end is disposed within the engine exhaust system to continuously sample exhaust gas within the exhaust system; (I7) an air intake pipe whose one end is open to the outside air;
(c) It has an exhaust gas metering orifice communicating with the exhaust gas sampling pipe and an air metering orifice communicating with the air intake pipe, and the sampling exhaust gas from the exhaust gas sampling pipe and the air from the air intake pipe are mixed at a predetermined ratio. (d) a mixed gas passage connected downstream of said mixing means; a catalytic converter disposed in the passageway for combustion; an oxygen sensor that outputs a proportional analog signal; (g) a heater disposed in the passageway upstream of the oxygen sensor to heat the exhaust gas mixture to a predetermined temperature; and (h) metering the exhaust gas and air, respectively. suction means for sucking the exhaust gas mixture in the passageway to mix the orifice and pass the exhaust gas mixture through the oxygen sensor;
heating means for heating the exhaust gas metering orifice so that suspended particles in the sampling exhaust gas are deflected from the surface of the exhaust gas metering orifice as the sampling exhaust gas passes through the exhaust gas metering orifice.

Since the heating means is provided to heat the exhaust gas metering orifice, the orifice is maintained at a higher temperature than the sampling exhaust gas flowing through it, and a temperature difference is created between the orifice surface and the exhaust gas flow. arise. The present invention utilizes the phenomenon of thermophoresis of particles caused by this temperature difference.
Particles suspended in the sampling exhaust gas are deflected in the exhaust gas stream from the hot orifice surface toward the cooler region in the center of the orifice, and pass through without colliding with the orifice surface, thereby preventing particle adhesion.

In a preferred embodiment of the invention, the orifice heating means is a heat exchanger! ! The heat exchanger is configured to heat the exhaust gas metering orifice with the sensible heat of the gas mixture. As is well known, the oxygen sensor is approximately 650
FS will function normally when the activation temperature range is maintained at ~750°C, and therefore the exhaust gas mixture will be heated to this temperature range by the heater when the temperature is low. ! It gets heated. In this embodiment, the sensible heat of the high-temperature exhaust gas/1% mixture is recovered and used to heat the exhaust gas metering orifice, so the structure of the detection unit can be simplified.

In another embodiment of the present invention, the mixed gas passageway and the mixing means in which the heater and the catalytic converter are housed are one
It is formed within one common metal block. According to this configuration, residual heat from the heater is transmitted to the exhaust gas metering orifice via the metal block, thereby heating the orifice more effectively.

〔Example〕

A first embodiment of the present invention will be described with reference to FIGS. 1 to 4. The air-fuel ratio measuring device is a detection unit of the present invention)l(B
= It is composed of a fuel cell 12, a heater controller 14, an air-fuel ratio calculation/display device 16, and a pressure gauge 18. The detection unit 10 samples exhaust gas from the exhaust system, mixes air with the sampled exhaust gas at a predetermined ratio, completely oxidizes the mixed gas, completely burns unburned components, and detects the residual oxygen concentration in the mixed gas. By doing so, an analog signal corresponding to the air-fuel ratio of the combustion air is displayed on the air-fuel ratio calculation display device 16.
It is configured to output to .

The detection unit 10 has a housing 24 fixed to a tail pipe 20 of an engine exhaust system by a clamp 22, and a stainless steel block 28 is held within the housing 24 via a heat insulating material filling 26. Inside the block 28 are an exhaust gas passage 30 and an air passage 3 which are parallel to each other.
2, a mixing mechanism 34 and a mixed gas passage 36 are formed.

Exhaust gas passage 30 and air passage 32 are connected to exhaust gas sampling tube 40 and air intake tube 42, respectively. As can be seen in FIG. 1, the upstream end 44 of the exhaust gas sampling tube 40 is inserted into the tailpipe 20 to sample a portion of the exhaust gas flowing within the tailpipe.

In order to offset the dynamic pressure and static pressure of the exhaust gas flowing inside the tail pipe 20 and introduce the exhaust gas at almost atmospheric pressure into the sampling pipe 40, a dynamic pressure boat 46 and a static pressure boat are installed at the upstream end 44 of the sampling pipe. 48 is the provision.

An upstream pipe 50 of the air intake pipe 42 is provided with an air intake boat 52 that is open to the atmosphere. Middle part 5 of air intake pipe 42
4 is curved into a U-shape and extends into the tail pipe 20. This intermediate portion 54 functions as a preheater that preheats the air using the heat of the exhaust gas flowing within the tail pipe 20.

Since the exhaust gas passage 30 and the air passage 32 are juxtaposed via a partition wall 58 having a plurality of horizontally extending heat exchange fins 56 (FIG. 1), the sampled exhaust gas flowing through these passages 30 and 32 is and air exchange heat with each other,
Both temperatures are equalized.

Mixing mechanism 34 has an exhaust gas metering orifice 60 and an air metering orifice 62. When a negative pressure is applied to the mixed gas passage 36 by a suction means such as a vacuum pump 64, the sampling exhaust gas and air are drawn into the sampling tube 40 and the air intake tube 42, respectively, and the passage 30,
32, the mixture reaches the orifices 60, 62 at almost atmospheric pressure, and is fed into the mixing chamber 6 at a predetermined flow rate while being metered by the orifices.
6 and mixed. Part of the mixed gas is in block 28
The mixed gas is discharged by the vacuum pump 64 through the discharge boat 68, and a portion thereof flows along the mixed gas passage 36.

An electric heater 70, a catalytic converter 72, a thermocouple 74, and an oxygen sensor 76 are arranged within the mixed gas passage 36. The output of the thermocouple 74 is sent to the heater controller 14
is input. This heater controller 14 has a thermocouple 7
The electric heater 70 is energized according to the temperature of the mixed gas detected in step 4, and the temperature of the mixed gas is controlled within the activation temperature range of the oxygen sensor 76. The catalytic converter 72 is a known type in which an oxidation catalyst such as platinum is supported on a carrier made of porous ceramic, and is used to completely burn unburned components in the mixed gas. The oxygen sensor 76 is of a known type made of a zirconia element, and detects residual oxygen in the mixed gas. An analog signal proportional to the solubility is output to the air-fuel ratio calculation/display device 16. As is well known, the oxygen sensor 76 has a built-in electric heater (not shown) that is controlled by the heater controller 14.
When the mixed gas temperature measured by the thermocouple 74 is lower than the activation temperature range of the oxygen sensor, the heater controller 1
4 energizes this built-in heater to heat the oxygen sensor 76.

Referring to FIGS. 2-4, block 28 is provided with a heat exchanger 78. As shown in FIGS. The heat exchanger 78 is comprised of heat exchange walls 80 , 82 surrounding the orifices 60 , 62 and passages 30 , 32 , and heating passages 84 , 86 . The upstream ends of the heating passages 84 and 86 are connected to the downstream ends of the mixed gas passage 36 by pipes 88 and 90, and the downstream ends are connected to the discharge pipe 96 by pipes 92 and 94.

The absolute pressure inside the discharge pipe 96 is measured by the pressure gauge 18,
The output is input to the air-fuel ratio calculation and display device 16. The air-fuel ratio calculation and display device 16 includes a microcomputer, converts the analog signal from the oxygen sensor 76 and the analog signal from the pressure gauge 18 into binary data, and calculates the air-fuel ratio using a predetermined calculation formula based on these data. It is programmed to calculate and display.

The operation of this detection unit and air-fuel ratio measuring device is as follows. When the vacuum pump 64 is activated, a portion of the exhaust gas is sampled by the sampling tube 40;
Fresh air is taken in through air intake pipe 42. This air is preheated by the preheating section 54. The air and the sampling exhaust gas flow through the passages 30 and 32 and exchange heat through the partition wall 58 to equalize the temperature, and the heat exchanger 7
8 heat exchange walls 80 , 82 through heating passages 84 ,
Heated by the mixed gas in 86, the orifice 60,
62 and mixed. The mixed gas is heated to about 650° C. by the heater 70, completely oxidized by the catalytic converter 72, and then comes into contact with the oxygen sensor 76. The oxygen sensor 76 outputs an analog signal corresponding to the residual oxygen concentration in the mixed gas to the air-fuel ratio calculation and display device 16. The air-fuel ratio calculation and display device 16 calculates and displays the air-fuel ratio of the combustion air-fuel mixture according to a given calculation formula based on the signals from the oxygen concentration sensor 76 and the pressure gauge 18. As the air-fuel ratio calculation formula, the formula described in the above-mentioned Japanese Patent Application Laid-Open No. 59-2-840 may be used, or other formulas may be used.

The high temperature mixed gas that has passed through the oxygen sensor 76 is transferred to a pipe 88.
, 90 to the heating passages 84, 86 of the heat exchanger 78.
The heat exchanger walls 80 and 82 in the vicinity of the orifices 60 and 62 are guided to the upstream end thereof, and the heat exchange walls 80 and 82 in the vicinity of the orifices 60 and 62 are guided to intensely heat and raise the temperature of these orifices. Additionally, residual heat from the heater 70 is transferred to the orifice 60 via the stainless steel block 28.
, 62 are further heated. As a result of the heating of the metering orifices 60, 62 to high temperatures, airborne particles, particularly carbon particles, in the sampling exhaust gas stream and the dosing air stream are deflected radially inward by thermophoretic effects towards the center of the flow passing through the orifices. be given Therefore, particle adhesion to the orifice surface is effectively prevented. In this way, the surface of the metering orifice, particularly the exhaust gas metering orifice 60, is kept clean and its inner diameter is kept constant, making it possible to accurately measure the air-fuel ratio.

After the mixed gas heats the metering orifices 60 and 62,
The heat exchange wall 80 flows through the heating passages 84 and 86.
, 82 to heat the incoming sampling exhaust gas and incoming air to the vacuum pump 64 via pipes 92 , 94 .
It is discharged by

FIG. 5 shows another embodiment of the detection unit. As in the first embodiment, the stainless steel block 128 includes an exhaust gas passage 130 communicating with an exhaust gas sampling pipe 140, and an exhaust gas passage 130 communicating with an exhaust gas sampling pipe 140. exhaust gas metering orifice 160 of the mechanism;
A mixed gas passage 136 is formed. Mixed gas passage 1
A heater 170, a catalytic converter 172, a thermocouple 174, and an oxygen sensor 176 are disposed within the catalytic converter 36. In this embodiment, the catalytic converter 172 is disposed upstream of the heater 170.

If the air-fuel ratio of the combustion mixture is too rich and a large amount of unburned components are present in the exhaust gas, the catalyst converter 172 may generate excessive heat, but this generated energy is transferred to the block 128. As the temperature of the mixed gas reaches the activation upper limit temperature of the oxygen sensor (approximately 7
50°C).

Therefore, if the heater 170 and the built-in heater of the oxygen sensor 176 are controlled by the heater controller, the temperature of the oxygen sensor can be more easily maintained within the activation temperature range.

〔Effect of the invention〕

Since the detection unit of the present invention has a heating means that deflects particles from the exhaust gas metering orifice by utilizing the thermophoretic phenomenon of floating particles, it is possible to actively prevent particles from adhering to the metering orifice. and enables accurate measurement of air-fuel ratio.

The embodiment in which the metering orifice is heated by a heat exchanger that recovers and utilizes the sensible heat of the mixed gas has a simple structure and does not require an extra energy source, so it is suitable for installation in an automobile engine. .

An embodiment in which the components of the detection unit are arranged in one common full-bending block has the advantage that residual heat from the heater can be used to further heat the metering orifice.

Furthermore, if the catalytic converter is placed upstream of the heater, temperature control of the oxygen sensor becomes easier.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an air-fuel ratio measuring device equipped with a detection unit of the present invention, in which the detection unit 71 is shown as a sectional view, other components of the air-fuel ratio measuring device are shown as a block diagram, and the second The figure is a -H view of the detection unit, Fig. 3 is a sectional view taken along the l1l-III arrow in Fig. 2, and Fig. 4 is a sectional view taken along the l1l-III arrow in Fig. 2.
FIG. 5, a sectional view taken along the V arrow, shows a second embodiment of the detection unit. DESCRIPTION OF SYMBOLS 10... Detection unit, 16... Air-fuel ratio calculation display device, 20... Tail pipe, 28... Metal block, 34... Mixing mechanism, 36... Mixed gas passage, 40... Exhaust gas sampling pipe, 42... Air intake pipe, 60... Exhaust gas meter is orifice, 62... Air measuring orifice, 64... Vacuum pump, 70... Heater, 72
...Catalytic converter, 76...Oxygen sensor, 78.
...Heat exchanger, 80, 82...Heat exchange wall.嬌2 roaizu, 3 replacement...r・4 ・:〕

Claims (1)

[Claims] 1. A detection unit used for outputting an analog signal according to the air-fuel ratio of a combustion mixture in an air-fuel ratio measuring device for measuring the air-fuel ratio of a combustion mixture in an internal combustion engine. (a) an exhaust gas sampling pipe whose one end is disposed within the engine exhaust system to continuously sample the exhaust gas within the exhaust system; (b) an air intake pipe whose one end is open to the outside air; (c) It has an exhaust gas metering orifice communicating with the exhaust gas sampling pipe and an air metering orifice communicating with the air intake pipe, and the sampling exhaust gas from the exhaust gas sampling pipe and the air from the air intake pipe are mixed at a predetermined ratio. mixing means for forming an oxygen-added exhaust gas mixture by mixing at the mixing means; (d) a mixed gas passage connected downstream of the mixing means; a catalytic converter disposed in the passageway for combustion; (g) a heater disposed in the passage upstream of the oxygen sensor to heat the exhaust gas mixture to a predetermined temperature; and (h) a metering orifice for directing the exhaust gas and air to respective metering orifices. suction means for suctioning the exhaust gas mixture in said passageway to mix and pass the exhaust gas mixture through the oxygen sensor; (i) sampling exhaust gas as the sampling exhaust gas passes through the exhaust gas metering orifice; heating means for heating the exhaust gas metering orifice to deflect suspended particles therein away from a surface of the exhaust gas metering orifice. 2. The detection unit according to claim 1, wherein the heating means comprises a heat exchanger adapted to heat the exhaust gas metering orifice with the sensible heat of the exhaust gas mixture after passing through the heater and the catalytic converter. . 3. The exhaust gas metering orifice and the air metering orifice are juxtaposed adjacent to each other, and the heat exchanger has a heat exchange wall surrounding both orifices.
Detection unit described in section. 4. The passage housing the heater and the catalytic converter and the mixing means are formed in one common metal block, and the exhaust gas metering orifice is further heated by the residual heat of the heater transmitted through the metal block. 3. A detection unit according to claim 3, wherein the detection unit is adapted to perform the following steps. 5. The detection unit according to claim 4, wherein the catalytic converter is arranged upstream of the heater. 6. In the metal block, an exhaust gas passage connecting the exhaust gas sampling pipe and the exhaust gas metering orifice and an air passage connecting the air intake pipe and the air metering orifice are formed parallel to each other and adjacent to each other, 5. A detection unit according to claim 4, wherein the heat exchange wall of the heat exchanger surrounds the exhaust gas passage and the air passage and is adapted to heat the sampled exhaust gas and air flowing therethrough.