JPH0746083B2 - Air-fuel ratio measuring device - Google Patents

Description

The present invention relates to an apparatus for measuring an air-fuel ratio of a combustion mixture by detecting a residual oxygen concentration for exhaust gas of an internal combustion engine using an oxygen concentration sensor. It is about.

[Conventional technology]

In the performance test and diagnosis of an internal combustion engine, it is necessary to measure the air-fuel ratio of the combustion mixture supplied into the cylinder. Conventionally, it has been known that the measurement of the air-fuel ratio is performed by detecting the residual oxygen concentration in the exhaust gas by using an oxygen concentration center arranged in the exhaust system. For example, JP-A-59-
In the air-fuel ratio measuring device disclosed in Japanese Patent No. 211840,
A known amount of oxygen is added to the exhaust gas collected from the exhaust system of the engine by mixing the fresh air taken from the outside at a predetermined ratio, and this mixed gas is sent to the oxidation catalyst device and the unburned components in the exhaust gas are added. After complete combustion, the residual oxygen concentration in the mixed gas is detected, and the detected residual oxygen concentration is substituted into a predetermined calculation formula to calculate the air-fuel ratio of the combustion mixture.

[Problems to be solved by the invention]

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

Also, in order to stabilize the output of the oxygen concentration sensor, it is necessary to maintain the sensor temperature at a high temperature of about 700 ° C, but with the conventional knowledge, a large thickness of heat insulating material is required to reduce the heat radiation loss, Therefore, there is a problem that the air-fuel ratio measuring device becomes large and this becomes an obstacle in mounting the vehicle.

[Means for solving problems]

The present invention solves the above-mentioned problems by providing a means for heat retention, exhaust fuel recovery, and fuel exchange using the heat of exhaust gas around the oxygen concentration sensor. That is, the configuration of the present invention for solving the above-mentioned problems, in the air-fuel ratio measuring apparatus for mixing the fresh air in the exhaust gas and detecting the residual oxygen concentration after the complete combustion of this mixed gas, around the oxygen concentration sensor. Is surrounded by a double wall composed of an annular passage through which the mixed gas passes, and a cylindrical exhaust heat recovery device through which the mixed gas passes is arranged on the outer circumference of the double wall. And a heat exchanger in which the exhaust gas passage and the fresh air passage are arranged close to each other.

[Work]

In the present invention having the above-mentioned configuration, the exhaust gas and the fresh air taken in from the outside are heat-exchanged by the heat exchanger to have a uniform temperature and mixed, and the mixed gas is completely burned through the catalyst and then oxygen is mixed. The concentration sensor detects the residual oxygen concentration in the mixed gas, and the air-fuel ratio of the combustion mixture is calculated based on the detected residual oxygen concentration. The high temperature gas mixture passing through the oxygen concentration sensor is
After passing through the heavy wall to keep it warm, the exhaust gas and fresh air flowing in the heat exchanger around the outer wall are heated while flowing through the exhaust heat recovery device, and 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. The air-fuel ratio measuring device comprises a detection unit 19, a battery 16, a heater controller 15, an air-fuel ratio calculation display device 14, and a pressure gauge 13. The detection unit 19 has a housing 10 fixed to a tail pipe 17 of an engine exhaust system by a clamp 18, and the stainless block 1 is held in the housing 10 via a heat insulating material filling 11. In the block 1, exhaust gas passages 101 and fresh air passages 102, which are close to each other and are alternately arranged so as to form a double helix, and a mixing mechanism 10.
5. An agitation mechanism 100, a double-walled heat insulation pipe 103, and an exhaust heat recovery device 104 are formed.

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

The upstream pipe 93 of the air intake pipe 9 is provided with an air intake port 92 opening to the atmosphere. The middle portion 91 of the air intake pipe 9 is bent 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,
It forms the 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 mixing mechanism 100 is provided in the mixed gas passage 107. This agitation mechanism 100 has a structure in which the direction of the mixed gas flow path is changed by 180 ° a plurality of times, and when the direction is changed, the flow path is rapidly contracted or expanded.

The double wall tube 103 and the exhaust heat recovery device 104 are arranged at positions that sequentially surround the mixed gas passage 107. Exhaust heat recovery unit 104 has 2
A plurality of fins are formed in the axial direction of the heavy-cylindrical passage to form a counterflow type heat exchanger with the double spiral flow passages 101 and 102 surrounding the exhaust heat recovery device 104.

The downstream end of the exhaust heat recovery device 104 is connected to the exhaust pipe 20. Discharge pipe 2
0 is connected to the vacuum pump 12.

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

Part of the exhaust gas flowing through the tail pipe 17 is collected from the upstream end 83 of the exhaust gas collecting pipe 8. At this time, the dynamic pressure and the static pressure of the exhaust gas flowing in the tail pipe 17 are canceled out, and the exhaust gas at almost atmospheric pressure is introduced into the sampling pipe 8, so that the sampling pipe upstream end 83 has a dynamic pressure port 81 and a static pressure. A pressure port 82 is provided.

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

The collected exhaust gas and fresh air flowing through the exhaust gas passage 101 and the air passage 102 forming the double helix exchange heat with each other through the partition wall forming the double helix, and the temperatures of the two are equalized, and at the same time, the exhaust heat is recovered. It exchanges heat with the vessel 104 and is preheated.

When a negative pressure is applied to the mixing chamber 106 by a suction means such as a vacuum pump 12, the sampling exhaust gas and the air are sucked into the sampling tube 8 and the air intake tube 9, respectively, and the passages 101 and 102 are taken.
After passing through, it reaches the orifices 4 and 5 at about atmospheric pressure, flows into the mixing chamber 106 at a predetermined flow rate and is mixed while being metered by the orifices.

The output of the thermocouple 7 provided in the mixed gas passage 107 is input to the heat controller 15. The heat 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. Catalytic converter 6
Is a known one in which an oxidation catalyst such as platinum is supported on a carrier made of a porous ceramic and completely burns unburned components in the mixed gas. The oxygen concentration sensor 2 is of a known type including a zirconia element, and an analog signal proportional to the residual oxygen concentration in the mixed gas is used as an air-fuel ratio calculation display device.
Output to 14. As is well known, the oxygen concentration sensor 2 has a built-in electric heater (not shown), and the heat controller 15
Is controlled to a constant output.

The stirrer 100 sufficiently stirs the mixed gas to eliminate the unevenness of the mixed gas to improve the output accuracy of the oxygen concentration sensor 2 and at the same time eliminate the uneven temperature of the mixed gas to improve the output accuracy of the thermocouple 7.

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

The exhaust heat recovery unit 104 is located outside the double wall tube 103, and the mixed gas that has passed through the double wall tube 103 flows into the exhaust heat recovery unit 104 and is located outside the exhaust heat recovery unit 104. Preheat the collected exhaust gas and air flowing through the spiral flow paths 101, 102. Here, by disposing the double-walled pipe 103, the exhaust heat recovery unit 104, and the double-helix flow passages 101, 102 having a lower temperature sequentially toward the outside with the oxygen concentration sensor 2 having the highest temperature as the center, heat radiation loss is reduced. It is decreasing.

The absolute pressure in the discharge pipe 20 is measured by the pressure gauge 13, and its output is input to the air-fuel ratio calculation display device 14. The air-fuel ratio calculation display device 14 includes a microcomputer, converts the analog signal from the oxygen concentration sensor 2 and the analog signal from the pressure gauge 13 into binary number data, and uses a predetermined calculation formula based on these data to empty the data. It is programmed to calculate and display the fuel ratio.

The operation of the detection unit 19 and the air-fuel ratio measuring device is as follows. When the vacuum pump 12 is operated, part of the exhaust gas is collected by the sampling pipe 8 and fresh air is taken in through the air intake pipe 9. This air is preheated by the preheating unit 91. Air and collected exhaust gas have a double helix structure and passage 10
While flowing in the inside of 1,102, heat is exchanged through the partition wall to make the temperature uniform, and at the same time, it is heated by the mixed gas of the exhaust heat recovery device 104 and passes through the orifices 4 and 5 to be 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 according to the residual oxygen concentration in the mixed gas to the air-fuel ratio calculation display device 14. The air-fuel ratio calculation display device 14 calculates and displays the air-fuel ratio of the combustion mixture according to a given calculation formula based on the signals from the oxygen concentration sensor 2 and the pressure gauge 13.

The formula for calculating the air-fuel ratio is shown below.

A / F = λ _e × (A / F) _t ... Formula (1) However, A / F ... air-fuel ratio (mass ratio definition) (A / F) _t ... theoretical air-fuel ratio λ _e ... oxygen excess ratio of exhaust gas λ _m ... oxygenation multiplication factor of mixed gas X ... air orifice and exhaust gas orifice Mass flow ratio (for the same gas under the same conditions) ρ _e ... Exhaust gas density (corresponding to λe) ρ _a ... Air density C _m ... Oxygen concentration in mixed gas C _A ... Oxygen concentration in air n … Regarding fuel components Number of hydrogen atoms per carbon atom P ₀₂ … Oxygen partial pressure in mixed gas at oxygen concentration sensor Pa… Absolute pressure of mixed gas at oxygen concentration sensor Fig. 2 shows the present invention 2 shows a block of the detection unit in the second embodiment of FIG.

In the second embodiment, the length of the exhaust heat recovery unit 104, the exhaust gas passage and the intake passages 101, 102 forming the double helix in the axial direction is extended, and the heater 3 and the outside of the stirring mechanism 100 are also surrounded. Thus, the effect of further reducing the heat radiation loss is obtained.

〔The invention's effect〕

The present invention provides a double wall disposed around an oxygen concentration sensor,
With the exhaust heat recovery device and the heat exchanger, the temperature of the oxygen concentration sensor can be kept constant and the measurement accuracy can be improved. Also, due to the arrangement structure around the oxygen concentration sensor, the temperature of the oxygen concentration sensor is maintained at a high temperature, so that the output can be stabilized and the air-fuel ratio measurement can be performed because a large thickness of heat insulating material is not required to maintain this high temperature. It is possible to avoid an increase in the size of the device, which is advantageous for mounting on a vehicle.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a first embodiment of the present invention, and FIG. 2 is a longitudinal 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.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Kamiya 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Japan Auto Parts Research Institute, Inc. (72) Inventor Kenichi Uchida 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Co., Ltd. (72) Inventor Masayuki Sawano 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd.

Claims (3)

[Claims] Claim: What is claimed is: 1. By mixing fresh air with exhaust gas collected from an exhaust system of an internal combustion engine to add oxygen to the exhaust gas and completely burning unburned components in the mixed gas, and then oxygen concentration. In an air-fuel ratio measuring device for detecting a residual oxygen concentration in the mixed gas by a sensor, the oxygen concentration sensor is surrounded by a double wall having an annular passage through which the mixed gas passes, and an outer periphery of the double wall. A cylindrical heat recovery unit through which the mixed gas passes, and a heat exchanger configured by disposing the exhaust gas passage and the fresh air passage in proximity to each other on the outer periphery of the exhaust heat recovery unit. An air-fuel ratio measuring device characterized by being provided. 2. The air-fuel ratio measuring device according to claim 1, wherein the exhaust heat recovery device is 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 is a heat exchanger having a double helix structure in which exhaust gas passages and fresh air passages are alternately arranged close to each other.