JPH0546899B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] 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.
More specifically, the present invention relates to a detection unit used in an air-fuel ratio measuring device to output an analog signal corresponding 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. It is also well known to detect the air-fuel ratio of the combustion mixture and control the fuel supply device so that the actual air-fuel ratio becomes a predetermined target air-fuel ratio (for example, the stoichiometric air-fuel ratio) depending on the engine operating conditions. .

Generally, the air-fuel ratio can be measured or detected by detecting the residual oxygen concentration 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 Patent Application Laid-Open No. 59-211840 solves this drawback. In this air-fuel ratio measurement device, exhaust gas is sampled from the engine exhaust system, and a known amount of oxygen is added to the sampled exhaust gas by mixing the sampled exhaust gas with fresh air taken in from the outside world at a predetermined ratio. be done. The mixture of exhaust gas and air is then sent to an oxidation catalyst device, where unburned components in the exhaust gas are completely combusted. The mixed gas oxidized in this way is brought into contact with an oxygen sensor, and the residual oxygen concentration is detected. By substituting the thus detected residual oxygen concentration into a predetermined calculation formula, the air-fuel ratio of the combustion air-fuel mixture can be determined. Since oxygen is added to the sampled exhaust gas in this way, it is possible to measure the air-fuel ratio of a superrich mixture that has an air-fuel ratio richer than the stoichiometric air-fuel ratio.

As disclosed in Japanese Patent Application Laid-Open No. 59-211840, a mixing mechanism equipped with a metering orifice is used to mix the sampling exhaust gas and the oxygen introduction air at a constant ratio. Since the flow rate of the fluid flowing through the metering 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 maintain a constant mixing ratio.
The inner diameter of the orifice is extremely small, typically approximately 1
mm. However, the sampling exhaust gas contains particles such as carbon, and these particles adhere to the exhaust gas metering orifice, causing the inner diameter of the orifice to change during metering, making it difficult to accurately measure the air-fuel ratio. There was a problem with it being a hindrance.

[Purpose of the invention]

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

[Summary of means and actions for solving problems]

The present invention provides a detection unit used in an air-fuel ratio measuring device to generate an analog signal in response to the air-fuel ratio of a combustion air-fuel mixture. This detection unit consists of (a) an exhaust gas sampling pipe whose one end is placed in the engine exhaust system to continuously sample the exhaust gas in the exhaust system, and (b) an air intake whose one end is open to the outside air. (c) an exhaust gas metering orifice communicating with the exhaust gas sampling tube and an air metering orifice communicating with the air intake tube, the sampled exhaust gas from the exhaust gas sampling tube and the air from the air intake tube. (d) a mixed gas passage connected downstream of the mixing means; and (e) unburned gas in the exhaust gas mixture. a catalytic converter disposed within the passageway for complete combustion of components; (f) contacting the exhaust gas mixture within the passageway downstream of the catalytic converter to detect residual oxygen in the exhaust gas mixture; an oxygen sensor that outputs an analog signal proportional to the concentration; (g) a heater disposed in the passageway upstream of the oxygen sensor to heat the exhaust gas mixture to a predetermined temperature; suction means for suctioning the exhaust gas mixture in said passageway to mix and pass the exhaust gas mixture through a metering orifice of said passage; and (i) when the sampling exhaust gas passes through the exhaust gas metering orifice. heating means for heating the exhaust gas metering orifice to deflect suspended particles in the sampling exhaust gas away from the surface of 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, and particles suspended in the sampling exhaust gas are deflected from the high-temperature orifice surface to the cooler area in the center of the orifice in the exhaust gas flow. Since it passes without colliding with the surface, adhesion of particles is prevented.

In a preferred embodiment of the invention, the orifice heating means comprises a heat exchanger, which heat exchanger is configured to heat the exhaust gas metering orifice with the sensible heat of the exhaust gas mixture. As is well known, oxygen sensors function normally when maintained at an activation temperature range of approximately 650-750°C, and for this reason the exhaust gas mixture must be heated to this temperature range by a heater when the temperature is low. be done. In this embodiment, the sensible heat of this hot exhaust gas mixture is recovered and used to heat the exhaust gas metering orifice, thereby simplifying the construction of the detection unit.

In a further embodiment of the invention, the mixed gas passages containing the heater and the catalytic converter and the mixing means are formed in 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 includes a detection unit 10, a battery 12, a heater controller 14, an air-fuel ratio calculation/display device 16, and a pressure gauge 18 according to the present invention. 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, it is configured to output an analog signal corresponding to the air-fuel ratio of the combustion air-fuel mixture to the air-fuel ratio calculation display device 16.

The detection unit 10 has a housing 24 fixed to a tailpipe 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 pad 26. Within the block 28 are formed an exhaust gas passage 30 and an air passage 32, a mixing mechanism 34, and a mixed gas passage 36, which are parallel to each other.

The exhaust gas passage 30 and the air passage 32 are
They are connected to an exhaust gas sampling pipe 40 and an air intake pipe 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 and is adapted 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 in the tail pipe 20 and introduce exhaust gas at approximately atmospheric pressure into the sampling pipe 40, a dynamic pressure port 46 and a static pressure port 48 are provided at the upstream end 44 of the sampling pipe. is provided.

An upstream pipe 50 of the air intake pipe 42 is provided with an air intake port 52 that is open to the atmosphere. The middle section 54 of the air intake tube 42 is curved in a U-shape and extends into the tailpipe 20. This middle part 5
4 acts as a preheater that preheats the air using the heat of the exhaust gas flowing inside 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, 32 is The air and air exchange heat with each other, and their temperatures become equal.

Mixing mechanism 34 includes an exhaust gas metering orifice 60 and an air metering orifice 62. vacuum pump 6
When a negative pressure is applied to the mixed gas passage 36 by a suction means such as 4, the sampling exhaust gas and air are sucked into the sampling pipe 40 and the air intake pipe 42, respectively, and pass through the passages 30, 32 to the orifice at approximately atmospheric pressure. 60, 62, and flows into the mixing chamber 66 at a predetermined flow rate while being metered by an orifice and is mixed. Part of the mixed gas goes to block 2
The mixed gas is discharged by the vacuum pump 64 through the discharge port 68 of 8, and a portion 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 input to the heater controller 14. The heater controller 14 energizes the electric heater 70 according to the temperature of the mixed gas detected by the thermocouple 74, and controls the temperature of the mixed gas 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 outputs an analog signal proportional to the residual oxygen concentration in the mixed gas to the air-fuel ratio calculation and display device 16. As is well known, the oxygen sensor 76 has a built-in electric heater (not shown) controlled by the heater controller 14, and when the mixed gas temperature measured by the thermocouple 74 is lower than the activation temperature range of the oxygen sensor, the heater is activated. The controller 14 energizes this built-in heater to heat the oxygen sensor 76.

Referring to FIGS. 2 to 4, block 28
A heat exchanger 78 is provided. This heat exchanger 7
8 indicates orifices 60, 62 and passages 30, 3
2, and heating passages 84, 86. Heating passages 84, 86
The upstream end of is connected to the downstream end of the mixed gas passage 36 by pipes 88, 90, and the downstream end is connected to the downstream end of the mixed gas passage 36 by pipes 88, 90.
94 connects to a discharge pipe 96.

The absolute pressure inside the exhaust pipe 96 is measured by the pressure gauge 18, and its output is input to the air-fuel ratio calculation/display device 16. The air-fuel ratio calculation/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 and fresh air is sampled by the air intake tube 4.
Incorporated from 2. This air is preheated by the preheating section 54. While the air and the sampling exhaust gas flow through the passages 30 and 32, they exchange heat through the partition wall 58 to equalize their temperature, and also pass through the heat exchanger 78.
Heating passage 84,
Heated by the mixed gas in 86, the orifice 6
0.62 and mixed. The mixed gas is heated to approximately 650°C by a heater 70, completely oxidized by a catalytic converter 72, and then sent to an oxygen sensor 76.
touch. 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 Laid-Open No. 59-211840 may be used, or other formulas may be used.

The high-temperature mixed gas that has passed through the oxygen sensor 76 is guided to the upstream ends of the heating passages 84 and 86 of the heat exchanger 78 via pipes 88 and 90, and is passed through the orifice 6.
It collides with the heat exchange walls 80 and 82 near 0 and 62, intensely heating these orifices and raising their temperature. In addition, the residual heat of the heater 70 is removed by the stainless steel block 2.
8 to further heat the orifices 60, 62. As a result of the high heating of the metering orifices 60, 62, airborne particles, particularly carbon particles, in the sampling exhaust gas stream and the dosing air stream are deflected radially inward by thermophoretic effects toward the center of the flow 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 heating the metering orifices 60, 62, the mixed gas flows through the heating passages 84, 86, heating the incoming sampling exhaust gas and incoming air through the heat exchange walls 80, 82, and passing through the pipes 92, 94. Afterwards, it is discharged by a vacuum pump 64.

FIG. 5 shows another embodiment of the detection unit, in which the stainless steel block 1 is similar to the first embodiment.
An exhaust gas passage 130 communicating with an exhaust gas sampling pipe 140, an exhaust gas metering orifice 160 of the mixing mechanism, and a mixed gas passage 136 are formed within the exhaust gas sampling tube 28. Inside the mixed gas passage 136 are a heater 170, a catalytic converter 172, a thermocouple 174,
Although an oxygen sensor 176 is disposed, in this embodiment, a 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 catalytic converter 172 may generate excessive heat, but this generated energy is transferred to the block 1.
Since the mixed gas is dissipated by heat transfer via 28, the temperature of the mixed gas does not exceed the activation upper limit temperature (approximately 750° C.) of the oxygen sensor 176. 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 suspended particles, it is possible to actively prevent particles from adhering to the metering orifice. Enables accurate measurement of air-fuel ratio.

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

An embodiment in which the components of the detection unit are arranged in one common metal 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 the drawing]

FIG. 1 is a schematic diagram of an air-fuel ratio measuring device equipped with a detection unit of the present invention. The detection unit is shown as a sectional view, other components of the air-fuel ratio measuring device are shown as a block diagram, and FIG. A top view of the unit, FIG. 3 is a sectional view taken along the - arrow in FIG. 2, FIG. 4 is a sectional view taken along the - arrow in FIG. 2, and FIG. 5 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 metering orifice,
62...Air metering orifice, 64...Vacuum pump, 70...Heater, 72...Catalytic converter,
76...Oxygen sensor, 78...Heat exchanger, 80,
82...Heat exchange wall.

Claims (1)

[Scope of Claims] 1. A detection unit used for outputting an analog signal according to the air-fuel ratio of the combustion mixture in an air-fuel ratio measuring device for measuring the air-fuel ratio of the combustion mixture of an internal combustion engine, , (a) an exhaust gas sampling pipe whose one end is placed in the engine exhaust system to continuously sample the exhaust gas in the exhaust system; (b) an air intake pipe whose one end is open to the outside air; c) It has an exhaust gas measuring orifice communicating with the exhaust gas sampling pipe and an air measuring 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. a mixing means for forming an oxygen-added exhaust gas mixture by mixing; (d) a mixed gas passage connected downstream of the mixing means; and (e) completely combusting unburned components in the exhaust gas mixture. (f) contacting the exhaust gas mixture in the passageway downstream of the catalytic converter to detect residual oxygen in the exhaust gas mixture and detecting a residual oxygen concentration proportional to the residual oxygen concentration; an oxygen sensor that outputs an analog signal; (g) a heater disposed in the passageway upstream of the oxygen sensor to heat the exhaust gas mixture to a predetermined temperature; suction means for suctioning the exhaust gas mixture in said passageway to mix and pass the exhaust gas mixture through the oxygen sensor; heating means for heating the exhaust gas metering orifice to deflect suspended particles of the exhaust gas metering orifice away from the surface of the exhaust gas metering orifice. 2. A detection unit as claimed in claim 1, comprising a heat exchanger adapted to heat an exhaust gas metering orifice with the sensible heat of the exhaust gas mixture after it has passed through the heater of the heating means and the catalytic converter. 3. The detection unit according to claim 2, wherein 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. 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: 5. The detection unit according to claim 4, wherein the catalytic converter is located 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. The detection unit of claim 4, wherein a heat exchange wall of a heat exchanger surrounds the exhaust gas passage and the air passage and is adapted to heat the sampled exhaust gas and air flowing therethrough.