JPS63168550A - Air/fuel ratio measuring apparatus - Google Patents

Abstract

PURPOSE:To miniaturize the equipment with the stabilization of an output of a sensor, by a method wherein the oxygen concentration sensor is surrounded by a double wall through which a mixed gas flows and a fresh air path is provided on the circumference of a waste heat recovery device so arranged on the circumference of the wall to let mixed gas pass. CONSTITUTION:Air taken in from an upstream tube 93 of an air intake pipe 9 is preheated at an intermediate position 91 by heat of an exhaust gas flowing through a tape pipe 17. A sampled exhaust gas and fresh air flowing through a double-spiralled exhaust gas path 101 and an air path 102 are subjected to a mutual heat exchange through a partition while a heat exchange takes place between the gas and air and an exhaust recovery device 104. With the suction of a mixing chamber 106 by a vacuum pump 12, the exhaust gas and air flow into the mixing chamber 106 being measured with orifices 4 and 5 via the pipes 8 and 9 and the paths 101 and 102 respectively. An output of a thermocouple 7 within a path 107 is inputted into a heater controller 15 to control the temperature of a mixed gas to the activation concentration range of an oxygen concentration sensor 2. A double wall tube 103 stabilizes the temperature thereof by the mixed gas flowing therethrough thereby achieving a higher output accuracy of the sensor 2.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an apparatus for measuring the air-fuel ratio of a combustion air-fuel mixture by detecting the residual oxygen concentration in the exhaust gas of an internal combustion engine using an oxygen concentration sensor. It is related to.

[Conventional technology]

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 into the cylinder. Conventionally, it is known that the air-fuel ratio is measured by detecting the residual oxygen concentration in the exhaust gas using an oxygen concentration sensor placed in the exhaust system6.
In the air-fuel ratio measuring device disclosed in Publication No. 211840, a known layer of oxygen is added to the exhaust gas collected from the engine exhaust system by mixing fresh air taken in from the outside world at a predetermined ratio. After the gas is sent to the oxidation catalyst device to completely burn the unburned components in the exhaust gas, the residual oxygen concentration in the mixed gas is detected, and the detected residual oxygen concentration is substituted into a predetermined formula for calculation. The air-fuel ratio of the combustion mixture is determined.

[Problem that the invention seeks to solve]

In order to improve the measurement accuracy of the air-fuel ratio measuring device using an oxygen concentration sensor as described above, it is necessary to keep the temperature of the oxygen concentration sensor constant, but due to changes in the temperature of the wall surrounding the sensor, The sensor temperature is affected,
There is a problem that measurement accuracy is reduced.

Furthermore, in order to stabilize the output of the oxygen concentration sensor, it is necessary to maintain the sensor temperature at a high temperature of approximately 700°C, but conventional devices require a large thickness of insulation material to reduce heat dissipation loss. Therefore, there is a problem in that the air-fuel ratio measuring device becomes large in size, which becomes an obstacle in mounting it on a vehicle.

[Means for solving problems]

The present invention solves the above problem by providing means for heat retention, exhaust heat recovery, and heat exchange using the heat of exhaust gas around the oxygen concentration sensor. That is, the configuration of the present invention for solving the above problems is such that, in an air-fuel ratio measuring device that mixes fresh air into exhaust gas and detects the residual oxygen concentration after complete combustion of this mixed gas, is surrounded by a double wall consisting of an annular passage through which the mixed gas passes, a cylindrical waste heat recovery device through which the mixed gas passes is arranged around the outer periphery of this double wall, and the outer periphery of this waste heat recovery device is The present invention is characterized in that a heat exchanger is disposed in which the exhaust gas passage and the fresh air passage are arranged close to each other.

[For production]

In the present invention having the above configuration, exhaust gas and fresh air taken in from the outside world are heat exchanged by a heat exchanger and mixed to a uniform temperature, and after this mixed gas is completely combusted via a catalyst, oxygen The concentration sensor detects the residual oxygen concentration in the mixed gas, and the air-fuel ratio of the combustion air-fuel mixture is calculated based on the detected residual oxygen concentration. The high temperature mixed gas that has passed through the oxygen concentration sensor is
After passing through the heavy wall and keeping it warm, the exhaust gas and fresh air flowing through the exhaust heat recovery device and the heat exchanger on the outer periphery are heated, and are then discharged to the outside. In this way, the temperature around the oxygen concentration sensor is kept constant and the temperature of this sensor is also kept high, which improves the measurement accuracy of the sensor and stabilizes its output.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention, and the air-fuel ratio measuring device includes a detection unit 19, a battery 16, a heater controller 15, an air-fuel ratio calculation display device 14, a pressure gauge 13
Consists of. The detection unit 19 has a housing 10 fixed to a tail pipe 17 of the engine exhaust system by a clamp 18, and a heat insulating material filling 11 is placed inside the housing 10.
A stainless steel block 1 is held through the holder. In the block 1 there are exhaust gas passages 101 and fresh air passages 102 arranged close to each other and alternating in a double helix, mixing tl! l structure 105, stirring mechanism 10
0, a double-walled heat-retaining pipe 103 and an exhaust heat recovery device 104 are formed.

Exhaust gas passage 101 and air passage 102 are connected to exhaust gas sampling pipe 8 and air intake pipe 9, respectively. An upstream end 83 of the exhaust gas sampling pipe 8 is inserted into the tail pipe 17, and a dynamic pressure boat 81 and a static pressure boat 82 are provided at the upstream end 83.

An upstream pipe 93 of the air intake pipe 9 is provided with an air intake boat 92 that is open to the atmosphere. The middle part 91 of the air intake pipe 9 is curved in a U-shape and extends into the tail pipe 17.

The exhaust gas passage 101 and the air passage 102 form a double helix and form a heat exchanger.

The mixing mechanism 105 has an exhaust gas metering orifice 4 and an air metering orifice 5.

Inside the mixed gas passage 107, an electric heater 3, a catalytic converter 6, a thermocouple 7, and an oxygen concentration sensor 2 are arranged.

A stirrer tR100 is provided in the mixed gas passage 107.

This stirring mechanism 100 rotates the direction of the mixed gas flow path by 180°.
, and has a structure in which the flow path suddenly contracts or expands when the direction changes.

The double-walled pipe 103 and the exhaust heat recovery device 104 are arranged at positions surrounding the mixed gas passage 107 one after another. Exhaust heat recovery device 1
04 is a double spiral passage 101 in which a plurality of fins are formed in the axial direction of a double cylindrical passage and surrounds an exhaust heat recovery device 104.
, 102 to form a counterflow type heat exchanger.

The downstream end of the exhaust heat recovery device 104 is connected to the exhaust pipe 20 . The exhaust pipe 20 is connected to the vacuum pump 12.

The detection unit 19 collects exhaust gas from the exhaust system, mixes fresh air in a predetermined ratio with the collected exhaust gas, adds oxygen, oxidizes this mixed gas, completely burns unburned components, and completes the mixture. By detecting the residual oxygen concentration in the gas, an analog signal corresponding to the air-fuel ratio of the combustion air-fuel mixture is output to the air-fuel ratio calculation/display device 14.

A portion of the exhaust gas flowing through the tail pipe 17 is sampled from the upstream end 83 of the exhaust gas sampling pipe 8 .

At this time, in order to offset the dynamic pressure and static pressure of the exhaust gas flowing inside the tail pipe 17 and introduce the exhaust gas at almost atmospheric pressure into the collection pipe 8, a dynamic pressure boat 81 is installed at the upstream end 83 of the collection pipe.
A hydrostatic boat 82 is provided.

The air taken in from the upstream pipe 93 of the air intake pipe 9 is preheated at the middle portion 91 of the air intake pipe by the heat of the exhaust gas flowing through the tail pipe 17 .

Exhaust gas passage 101 and air passage 102 forming a double helix
The sampled exhaust gas and fresh air flowing through exchange heat with each other through the partition wall forming a double helix, and the temperature of both is equalized, and at the same time, heat is exchanged with the exhaust heat recovery device 104,
Preheated.

When a negative pressure is applied to the mixing chamber 106 by a suction means such as a vacuum pump 12, the sample exhaust gas and air are drawn into the sample tube 8 and air intake tube 9, respectively, and into the passage 10.
1 and 102, it reaches the orifice 4.5 at approximately atmospheric pressure, and flows into the mixing chamber 106 at a predetermined flow rate while being metered by the orifice, where it is mixed.

The output of the thermocouple 7 provided in the mixed gas passage 107 is input to the heater controller 15. This heater controller 15 controls the temperature of the mixed gas detected by the thermocouple 7 within the activation temperature range of the oxygen concentration sensor 2. The catalytic converter 6 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 concentration sensor 2 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 display device 14.As is well-known, the oxygen concentration sensor 2 is an electric heater. (not shown), and is controlled to a constant output by a heater controller 15.

The stirring mechanism 100 sufficiently stirs the mixed gas, eliminates uneven mixing of the mixed gas, improves the output accuracy of the oxygen concentration sensor 2, and at the same time eliminates temperature unevenness of the mixed gas and improves the output accuracy of the thermocouple 7.

The double-walled tube 103 has a structure having an annular passage so that the mixed gas passes through the inner wall and then flows on the outside thereof, and the temperature change in the double-walled tube 103 is reduced due to the heat retention effect of the mixed gas. The output accuracy of the oxygen concentration sensor 2, which is greatly affected by the surrounding wall temperature, is improved.

The exhaust heat recovery device 104 is located outside the double wall pipe 103,
The mixed gas that has passed through the double wall pipe 103 is sent to the exhaust heat recovery device 104
The sampled exhaust gas and air flowing through the double helix channels 101 and 102 located outside the waste heat recovery device 104 are preheated. Here, starting from the oxygen concentration sensor 2 with the highest temperature, the double-walled tubes 10 with lower temperatures are sequentially moved outward.
3. Exhaust heat recovery device 104.2 double spiral flow path 101, 10
2 reduces heat radiation loss.

The absolute pressure inside the discharge pipe 20 is measured by the pressure gauge 13,
The output is input to the air-fuel ratio calculation and display device 14. The air-fuel ratio calculation and display device 14 includes a microcomputer, and receives an analog signal from the oxygen concentration sensor 2 and a pressure gauge 13.
It is programmed to convert the analog signal from the controller into binary data, calculate and display the air-fuel ratio using a predetermined calculation formula based on these data.

The operation of this detection unit 19 and air-fuel ratio measuring device is as follows. When the vacuum pump 12 is activated, a portion of the exhaust gas is sampled via the sampling tube 8 and fresh air is taken in via the air intake tube 9.

This air is preheated by the preheating section 91. The air and the sampled exhaust gas flow through the double-helix structure passages 101 and 102 and exchange heat through the partition walls to equalize the temperature, and are heated by the mixed gas in the exhaust heat recovery device 104, and then pass through the orifice 4. 5 and mixed. The mixed gas is completely oxidized by the catalytic converter 6, heated to about 650° C. by the heater 3, sufficiently stirred by the stirring mechanism 100, and brought into contact with the oxygen concentration sensor 2. The oxygen concentration sensor 2 outputs an analog signal corresponding to the residual oxygen concentration in the mixed gas to the air-fuel ratio calculation and display device 14. The air-fuel ratio calculation and display device 14 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 2 and the pressure gauge 13.

The air-fuel ratio calculation formula is shown below.

A/F= person, X(A/Fb
...Formula (I) However, A/F...Air-fuel ratio (mass ratio definition) (A/F)t...Theoretical air-fuel ratio^8...Oxygen excess rate of exhaust gas^,...Mixture Oxygen excess ratio of gas Density C, I...Oxygen concentration in mixed gas CA...Oxygen concentration in air η...Number of hydrogen atoms per carbon atom for fuel components PO2...At oxygen concentration sensor section Oxygen partial pressure Pcl in the mixed gas: Absolute pressure of the mixed gas at the oxygen concentration sensor section FIG. 2 shows a block of the detection unit in the second embodiment of the present invention.

In the second embodiment, the exhaust heat recovery device 104.2 has a structure in which the axial length of the double spiral exhaust gas passage and air passages 101 and 102 is extended to also surround the outside of the heater 3 and the stirring mechanism 100. By doing so, it is possible to obtain the effect of further reducing heat radiation loss.

〔Effect of the invention〕

The present invention provides a double wall arranged around an oxygen concentration sensor,
The exhaust heat recovery device and the heat exchanger keep the temperature of the oxygen concentration sensor constant and improve its measurement accuracy. In addition, due to the arrangement structure around the oxygen concentration sensor mentioned above, the temperature of the oxygen concentration sensor is maintained at a high temperature, which makes it possible to stabilize the output, and because it does not require a large thickness of insulation material to maintain this high temperature, it is possible to measure the air-fuel ratio. It is possible to avoid increasing the size of the device, which is advantageous for mounting on a vehicle.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of a first embodiment of the present invention, and FIG. 2 is a longitudinal cross-sectional view of a main part of a second embodiment of the present invention. 1...Detection unit block, 2...Oxygen concentration sensor, 6...Catalytic converter, 8
...Exhaust gas sampling pipe, 9...Air intake pipe, 12...
・Vacuum pump, 13... Pressure gauge, 14... Air-fuel ratio calculation display device, 15... Heater controller, 16... Battery, 19... Detection unit,
20...Exhaust pipe, 101...Exhaust gas passage,
102...Air passage, 103...Double wall pipe,
104...Exhaust heat recovery device, 105...Mixing mechanism,
106... Mixing chamber, 107... Mixed gas passage.

Claims (1)

[Claims] 1. After adding fresh air to the exhaust gas collected from the exhaust system of an internal combustion engine and adding oxygen to the exhaust gas, and completely burning the unburned components in this mixed gas. , an air-fuel ratio measuring device for detecting the residual oxygen concentration in the mixed gas using an oxygen concentration sensor, the oxygen concentration sensor being surrounded by a double wall having an annular passage through which the mixed gas passes; A cylindrical exhaust heat recovery device through which the mixed gas passes is provided on the outer periphery of the wall, and the exhaust gas passage and the fresh air passage are arranged close to each other on the outer periphery of the exhaust heat recovery device. An air-fuel ratio measuring device characterized by being equipped with an exchanger. 2. The air-fuel ratio measuring device according to claim 1, wherein the exhaust heat recovery device is formed of a cylindrical body having a plurality of fins in the axial direction. 3. The air-fuel ratio measuring device according to claim 1, wherein the heat exchanger has a double helical structure in which exhaust gas passages and fresh air passages are arranged close to each other alternately.