JPH0546894B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an air-fuel ratio measuring device using a current detection type oxygen concentration sensor having a diffusion resistance layer, and particularly relates to an air-fuel ratio measuring device suitable for use in an automobile engine. Regarding sensors.

[Prior art and problems]

It is well known that the residual oxygen concentration in internal combustion engine exhaust gas is detected by a sensor and the air-fuel ratio of the combustion air-fuel mixture is controlled accordingly. This type of measuring device is defined as an air-fuel ratio measuring device.

Air-fuel ratio measurement devices used today can be broadly classified into two types. The first measuring device outputs a lean or rich signal depending on the presence or absence of residual oxygen in the exhaust gas. With this measuring device,
If the air-fuel ratio of the air-fuel mixture is richer than the stoichiometric air-fuel ratio and there is no residual oxygen in the exhaust gas, the air-fuel ratio cannot be measured.

A second type of measuring device eliminates this drawback and is disclosed, for example, in Japanese Patent Application Laid-Open No. 59-211840. In this device, the exhaust gas sampled from the engine exhaust system is diluted with fresh air at a predetermined ratio, oxygen is added to the sampled exhaust gas at a predetermined ratio, and the oxygen concentration in the sampled exhaust gas thus diluted is determined. is detected by an oxygen concentration sensor. The present invention relates to this second type of air-fuel ratio measuring device.

The sampling exhaust gas and the dilution air are mixed using a capillary tube (Japanese Patent Laid-Open No. 59-211840) or an orifice. In order to maintain a constant mixing ratio, the temperature and pressure differences between the sampling exhaust gas stream and the dilution air stream must be minimized upstream of the mixing section. Temperature equalization of the sampling exhaust gas stream and the dilution air stream can be achieved using a heat exchanger.

On the other hand, in order to equalize the pressure, conventional air-fuel ratio measuring devices use a variable throttle or the like, which is one of the causes of increasing the size and complexity of the device.

[Purpose of the invention]

It is an object of the present invention to have a compact and simple structure, and to completely equalize the pressure of the sampling exhaust gas stream and the pressure of the dilution air stream before dilution to maintain the dilution rate at a desired value. The object of the present invention is to provide a possible air-fuel ratio measuring device.

[Summary of means and actions for solving problems]

The present invention exchanges heat between a sampled exhaust gas sampled from an internal combustion engine exhaust system through a sampling pipe and dilution air taken in through a dilution air supply pipe, and separates the sampled exhaust gas flow and the dilution air flow. In an air-fuel ratio measuring device that dilutes sampling exhaust gas by mixing it at a predetermined ratio and detects the oxygen concentration in the thus diluted sampling exhaust gas with an oxygen concentration sensor, the tip of the sampling pipe is connected to the engine exhaust gas. The dynamic pressure port is placed in the tailpipe of the system, and the tip of this port has a dynamic pressure port placed so that the dynamic pressure of the exhaust gas flow flowing through the tailpipe acts, and a dynamic pressure port placed so that the static pressure of the exhaust gas flow acts on it. A static pressure port is provided, and the opening area of the static pressure port is larger than the opening area of the dynamic pressure port. The opening area of the static pressure port is approximately 4 times the opening area of the dynamic pressure port.
Preferably, it is doubled.

The dynamic pressure of the exhaust gas flow acting on the dynamic pressure port is a positive pressure compared to atmospheric pressure, and the static pressure of the exhaust gas flow acting on the static pressure port has a negative value compared to atmospheric pressure. Therefore, the dynamic pressure and static pressure cancel each other out, and the pressure of the sampling exhaust gas in the sampling pipe becomes approximately atmospheric pressure. On the other hand, the pressure of the dilution air in the dilution air supply pipe is atmospheric pressure. Therefore, the sampling exhaust gas flow at atmospheric pressure and the dilution air flow are always supplied to the mixing section of the air-fuel ratio measuring device without being affected by fluctuations in engine operating conditions, so the mixing ratio remains constant. is maintained.

〔Example〕

Referring to FIG. 1, an air-fuel ratio measuring device 10 of the present invention has a housing 16 attached to a tail pipe 12 of an engine exhaust system with a clamp 14. A heat exchanger 20 and a stainless steel block 22 are disposed within the housing 16 via an insulating material filling 18.
is located. Inside the block 22 is a mixing section 2.
4, and downstream thereof, a catalyst device 26 for completely oxidizing unburned components in the exhaust gas,
A temperature detection thermocouple 28 and an oxygen concentration sensor 30 are arranged. The output of the thermocouple 28 is input to the heater controller 32, and the output of the sensor 30 is input to the air-fuel ratio calculation/display device 34. As is well known,
The oxygen concentration sensor 30 has a built-in electric heater (not shown), and the heater controller 32 energizes the heater when the temperature of the mixed gas detected by the thermocouple 28 is lower than the activation temperature of the sensor 30, which is about 600°C. The temperature of the oxygen concentration sensor 30 is maintained at the activation temperature. The air-fuel ratio calculation display device 34 is
A signal from the absolute pressure gauge 36 that detects the absolute pressure of the mixed gas near the sensor 30 and the oxygen concentration sensor 30
It is configured to calculate and display the air-fuel ratio based on signals from the air-fuel ratio. A battery 3 is installed in the heater controller 32, pressure gauge 36, and air-fuel ratio calculation/display device 34.
Power is supplied from 8.

The dilution air introduction system consists of a dilution air intake pipe 40 made of stainless steel. This intake pipe 40
The downstream end communicates with the orifice 42 via the heat exchanger 20, and the upstream end communicates with the port 44.
is installed to let in the atmosphere.

The exhaust gas sampling system is comprised of a stainless steel sampling pipe 46. The downstream end of this sampling pipe 46 communicates with an orifice 48 via a heat exchanger 20.

An upstream tip 50 of the sampling pipe 46 is disposed within the tailpipe 12. In accordance with the present invention, this tip 50 is provided with a dynamic pressure port 52 and a static pressure port 54. Dynamic pressure port 52
is the flow of exhaust gas in the tailpipe 12 (arrow 5
6), and converts the dynamic pressure of the exhaust gas flow into static pressure as described later. The static pressure port 54 opens in a direction perpendicular to the flow of exhaust gas, so that only the static pressure acts thereon without being affected by the dynamic pressure of the exhaust gas flow. In the illustrated embodiment, four static pressure ports 54 are provided, but the number can be increased or decreased. It is desirable that the total opening area of the static pressure ports 54 be approximately four times the opening area of the dynamic pressure ports 52.

Intake sampling exhaust gas and dilution air,
A vacuum pump 58 is provided to mix the two gases by passing through the orifices 42 and 48, and to discharge the mixed gas after measuring the oxygen concentration.

The operation of this air-fuel ratio measuring device 10 is as follows.

When the vacuum pump 58 is activated, dilution air is supplied from the supply pipe 40 and exhaust gas is supplied from the sampling 4.
Introduced from 6. After they exchange heat in the heat exchanger 20 and reach a uniform temperature, they flow into the mixing chamber 24 through orifices 42 and 48, where they are mixed and diluted, processed by the catalyst device 26, and then connected to the oxygen concentration sensor. 30, the oxygen concentration is measured.

In the above operation, in order to keep the mixing ratio of sampling exhaust gas and dilution air constant regardless of engine operating conditions, orifices 42 and 4
It is very important to equalize the pressure of the sampling exhaust gas and the dilution air upstream of the 8. In the device of the invention this is achieved based on the following principle.

Since the exhaust gas flowing inside the tail pipe 12 has a flow velocity, its pressure can be considered to consist of dynamic pressure and static pressure. The dynamic pressure in the tailpipe takes a positive value compared to atmospheric pressure, and the static pressure takes a negative value.

As mentioned above, the purpose of the dynamic pressure port 52 is to take in this dynamic pressure, and the exhaust gas flow collides with the tip end surface of the tip end 50 of the sampling pipe 46 as shown by the arrow 56 and loses its flow velocity. The dynamic pressure is converted into positive static pressure, the latter acting in the pipe tip 50 via the dynamic pressure port 52.

On the other hand, since the static pressure port 54 is arranged so as to be affected only by static pressure, static pressure having a negative value acts within the tip of the pipe. Therefore, the positive static pressure (converted from the dynamic pressure) and the negative static pressure cancel each other out within the pipe tip 50. It has been found that in a typical internal combustion engine, the ratio of positive static pressure to negative static pressure is approximately 4:-1. Therefore, if the total opening area of the static pressure ports 54 is made approximately four times the opening area of the dynamic pressure ports 52, the pressure inside the sampling pipe 46 will be approximately atmospheric pressure regardless of pressure fluctuations inside the tail pipe 12. can be understood.

On the other hand, the port 44 of the dilution air supply pipe 40
The pressure of the dilution air taken in from is atmospheric pressure.

In this way, dilution air and sampling exhaust gas at approximately atmospheric pressure are supplied to the orifices 42 and 48, respectively, and the dilution air and sampling exhaust gas are supplied to the orifices 42 and 48 at a predetermined rate determined by the dimensions of the orifices. mixed in proportion.

FIG. 2 shows a variation of the tip of the sampling pipe 46. In this embodiment, the tip is constituted by a head 62 that is separate from the rest of the sampling pipe 60, and this head 62 has a dynamic pressure port 5.
2 and a static pressure port 54 are provided. Since this head 62 is attached to the remaining pipe portion 60 by screwing, there is an advantage that even if the exhaust gas characteristics change depending on the type of automobile, it can be dealt with simply by replacing the head 62.

〔Effect of the invention〕

As described above, according to the present invention, the pressures of the dilution air and the sampling exhaust gas are equalized on the upstream side of the orifices 42 and 48 (both substantially at atmospheric pressure), regardless of pressure fluctuations in the exhaust system. ) can be done. Therefore, the dilution ratio can be maintained constant, and the accuracy of air-fuel ratio measurement can be improved.

Moreover, the pressure equalization mechanism of the present invention is extremely simple, can be implemented at low cost, and contributes to downsizing of the measuring device.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the air-fuel ratio measuring device of the present invention, and FIG. 2 shows a variation of the sampling pipe. 10... Air-fuel ratio measuring device, 12... Tail pipe, 20... Heat exchanger, 24... Mixing chamber, 30...
...Oxygen concentration sensor, 40... Dilution air supply pipe, 42, 48... Orifice, 46... Sampling pipe, 50... Tip of sampling pipe, 52... Dynamic pressure port, 54... Static pressure port.

Claims (1)

[Scope of Claims] 1. Heat exchange between sampled exhaust gas sampled from an internal combustion engine exhaust system through a sampling pipe and dilution air at approximately atmospheric pressure taken in via a dilution air supply pipe, and the sampled exhaust gas In the air-fuel ratio measuring device, the sampling exhaust gas is diluted by mixing a dilution air flow and a dilution air flow at a predetermined ratio, and the oxygen concentration in the thus diluted sampling exhaust gas is detected by an oxygen concentration sensor. The tip of the sampling pipe is arranged in the tail pipe of the engine exhaust system, and the tip has a dynamic pressure port on which the dynamic pressure of the exhaust gas flow flowing in the tail pipe acts, and a dynamic pressure port on which the dynamic pressure of the exhaust gas flow flowing in the tail pipe acts. 1. An air-fuel ratio measuring device comprising: a static pressure port on which static pressure acts, and the opening area of the static pressure port is larger than the opening area of the dynamic pressure port. 2. The air-fuel ratio measuring device according to claim 1, wherein the opening area of the static pressure port is approximately four times the opening area of the dynamic pressure port. 3. The air-fuel ratio measuring device according to claim 2, wherein the tip of the sampling pipe is formed separately from the remainder of the sampling pipe, and the tip is detachably attached to the remainder.