JPS6333100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that can measure an air-fuel ratio from the contents of carbon monoxide, carbon dioxide, and hydrocarbons contained in engine exhaust gas.

Conventionally, in order to measure the air-fuel ratio based on the contents of carbon monoxide, carbon dioxide, and hydrocarbons contained in exhaust gas, this air-fuel ratio is expressed as a function of the content of each of the above compounds. That is what is being attempted.

Therefore, if the contents of carbon monoxide, carbon dioxide, and hydrocarbons in exhaust gas are known, the air-fuel ratio can be determined, but in general, the response of an analyzer that detects the contents of each of the above compounds is The speed is fast for those for carbon monoxide and slow for those for carbon dioxide and hydrocarbons, so a phase shift occurs in the detected waveform, and as a result, the output from each analyzer is directly input to a calculator, etc. In this case, there was a problem that a large measurement error occurred.

The present invention aims to solve these problems, and includes an analyzer that analyzes carbon monoxide, carbon dioxide, and hydrocarbons contained in exhaust gas to detect each content, and an analyzer that detects each content. A low-pass filter having a time constant larger than the response time of the analyzer is interposed between the analyzer and the calculator. The response speed of the carbon monoxide analyzer is faster than that of the carbon dioxide and hydrocarbon analyzers, but it is larger than the response time of each analyzer. Since a low-pass filter having a time constant is provided, the detection signal from each analyzer is smoothed by the low-pass filter and sent to the arithmetic unit, thereby preventing measurement errors from occurring.

Below, an air-fuel ratio measuring device as an embodiment of the present invention will be explained with reference to the drawings. In order to explain its operation, FIG. 1 shows the respective contents of carbon monoxide and carbon dioxide contained in engine exhaust gas. Figure 2 is a graph showing the relationship between the air-fuel ratio and the content of hydrocarbons contained in engine exhaust gas to explain its effect. Figure 3 is the electrical circuit. Figures 4 and 5 are schematic diagrams showing the analyzer, and Figures 6a and 6b are waveform diagrams for explaining its operation.

In general, the relationship between carbon monoxide contained in engine exhaust gas and the air-fuel ratio and the relationship between carbon dioxide and the air-fuel ratio are shown in Figure 1 with the symbols CO and _CO2, respectively.
It is also known that the relationship between the total hydrocarbons contained in the exhaust gas and the air-fuel ratio is as shown in FIG. 2 with the symbol THC.

Here, in FIGS. 1 and 2, the symbol AFR ₀ indicates the optimum air-fuel ratio, and the value becomes larger toward the right side of the optimum air-fuel ratio AFR ₀ in each figure. That is, the further to the right, the leaner state the proportion of the mixed fuel is, and the further to the left, the richer the proportion of the mixed fuel becomes.

The unit of carbon monoxide and carbon dioxide content is %, and the unit of hydrocarbon content is volume ppm.

Therefore, if the contents of carbon monoxide, carbon dioxide, and hydrocarbons contained in exhaust gas are known from Figures 1 and 2, the air-fuel ratio can also be determined, but the inventor studied conventional research reports. As a result, the air fuel ratio
It has been found that there is no problem in expressing AFR as a function with the content of each of the above compounds as a variable as shown in formula (1).

AFR=208.8−{1.83(CO)+3.05(THC)}/(CO)+
(CO ₂ )+(THC)+0.96...(1) However, the carbon-to-water ratio m/n of the fuel C _o H _n is 1.85.

In moss, (CO) is a percentage value indicating the content of carbon monoxide contained in exhaust gas, (CO ₂ )
is a percentage value indicating the content of carbon dioxide contained in the exhaust gas, and (THC) is a percentage value indicating the content of hydrocarbons contained in the exhaust gas in terms of methane.

Hereinafter, it will be explained in detail that the analog computing unit AO is configured to be able to compute the above-mentioned equation (1) and that the air-fuel ratio AFR can be determined.

As shown in FIG. 4, a non-dispersive infrared analyzer 1 is provided which can analyze carbon dioxide contained in exhaust gas and detect the content of carbon dioxide in the exhaust gas.

This analyzer 1 includes an infrared light emitter 1a, a chopper 1b that allows light from the light emitter 1a to pass through at predetermined intervals, and a chopper 1b that allows only a predetermined absorption line wavelength of the light from the light emitter 1a to pass through. A sample chamber 1d which is equipped with a water-containing optical filter 1c and through which a sample gas (carbon dioxide) can flow, a gas chamber 1e filled with the same gas as the sample gas, and a gas chamber 1e adjacent to the gas chamber 1e. The sensor 1f is configured to include a sensor 1f that can output the carbon dioxide content in exhaust gas as an analog electrical signal.

Since this non-dispersive infrared analyzer 1 is configured in this way, when carbon dioxide in the exhaust gas is passed to the sample chamber 1d, the carbon dioxide in the exhaust gas absorbs a portion of the infrared rays, so that Gas filling chamber 1
Since the amount of infrared absorption at e is reduced compared to the case where the exhaust gas is not passed through the sample chamber 1d, this amount of reduction can be detected by the sensor 1f and the content of carbon dioxide in the exhaust gas can be measured.

Note that this sensor 1f outputs an analog voltage signal of an amount corresponding to the content of carbon dioxide in the exhaust gas.

Furthermore, an analyzer with a sensor 1'f capable of analyzing carbon monoxide in the exhaust gas and detecting the content of carbon monoxide in the exhaust gas is provided. The same type of non-dispersive infrared analyzer is used.

Further, as shown in FIG. 5, a flame ionization type analyzer 2 is provided which can analyze hydrocarbons contained in the exhaust gas and detect the content of hydrocarbons in the exhaust gas. To detect the hydrocarbon content in exhaust gas using this analyzer 2, exhaust gas containing hydrocarbons is supplied to the hydrogen flame 2a through the pipe 2b, and the ionic current generated thereby is detected by the sensor 2c. Detection is performed.

Note that this sensor 2c also outputs an analog voltage signal of an amount corresponding to the content of hydrocarbons in the exhaust gas.

By the way, the response speed of each of the above analyzers is fast for carbon monoxide and slow for carbon dioxide and hydrocarbons, as described above.

Here, to give an example, FIG. 6a is a waveform diagram showing the input/output response of carbon dioxide. In the case of carbon dioxide, since the response speed of the analyzer 1 is slow,
The input waveform a shown by the solid line in Fig. 6a and the output waveform b shown by the same chain line are out of phase, and as a result, the output waveform b is used as the output waveform c of carbon monoxide shown in Fig. 6b, which will be described later. Inputting it to the calculator AO will cause a measurement error.

Therefore, in order to eliminate errors due to differences in response speed of each analyzer, each sensor 1f, 1'f,
As shown in FIG. 3, the output from 2c is input to low-pass filters 3, 3, and 3 each having a time constant longer than the response time of each of the above-mentioned analyzers.

Each filter 3 is composed of a resistor R and a capacitor C, and an electrolytic capacitor can also be used as the capacitor C.

The output from each filter 3 is input to an analog computing unit AO via buffer amplifiers 4, 4, 4, respectively.

Note that each buffer amplifier 4 is composed of an operational amplifier, and in this case, the filter 3 and buffer amplifier 4 constitute an active filter.

In this way, each analog signal input to the analog computing unit AO is sent to the semi-fixed resistance groups R ₁ , R ₂ , R ₃ and the semi-fixed resistance groups R ₄ , R ₅ connected in parallel with each other. It is selectively input as appropriate.

That is, analog signals corresponding to the respective contents of carbon dioxide, carbon monoxide, and hydrocarbons are input to the semi-fixed resistance groups R ₁ , R ₂ , and R ₃ , and here the above-mentioned equation (1) is calculated. One term denominator i.e. {(CO)+(CO ₂ )+
(THC)} is calculated, and the semi-fixed resistance group R ₄ ,
Analog signals corresponding to each content of carbon monoxide and hydrocarbon are input to R ₅ , and here, a part of the molecule in the first term of formula (1), that is, {1.83 (CO) + 3.05 (THC)}
calculations are performed.

As a result, each of the semi-fixed resistance groups R ₁ to _{R 3} ;R ₅ has a function as an additive attenuator.

In addition, in this calculator AO, the content of carbon monoxide is 10% or 12%, and the content of carbon dioxide is 16%.
are further adjusted such that each 1% hydrocarbon content corresponds to a voltage signal of 1 volt.

Furthermore, it goes without saying that a variable resistor or a resistor having a predetermined resistance value can be used instead of the semi-fixed resistor group R ₁ to R ₅ .

Next, the summed outputs from the semi-fixed resistance groups R ₁ to _{R 3} are amplified by an amplifier 5 and then input to a divider 6 .

Also, the addition output from the semi-fixed resistance groups R ₄ and R ₅ is
The signal from the summing amplifier 7 is inverted and added to the signal corresponding to 208.8 as a part of the first term numerator of the equation (1) from the potentiometer 8. A signal corresponding to the 1-term numerator is output, and then this output signal is input to the divider 6.

The signal input to the divider 6 in this way is
Here, the first term of equation (1), 208.8−{1.83(CO)+3.05(THC)}/(CO)+(CO
₂ ) + (THC) calculation is performed.

Further, the signal from the divider 6 is inverted by the adder 9 and added to the signal from the potentiometer 10 corresponding to 0.96 as the second term of equation (1), so that from this adder 9, Formula (1), i.e. air-fuel ratio AFR
A signal corresponding to is output.

The signal output from the adder 9 is input to a pen recorder or indicator (not shown), where the air-fuel ratio is determined.
AFR is displayed.

Therefore, the apparatus of this embodiment has the advantage of being able to quickly and accurately measure the air-fuel ratio with a simple structure while eliminating the problems caused by the differences in response time of each analyzer.

In addition, as in the above-mentioned embodiment, as an arithmetic unit,
Instead of using an analog computing unit, a digital computing unit may be used.

In this way, a digital arithmetic unit may be used.

Even when a digital calculator is used in this way, the phase shift of the output from the analyzer is smoothed by filter 3 before being input to the calculator, making it possible to significantly reduce measurement errors. I can,
Accurate air-fuel ratio measurement can be performed.

As detailed above, according to the air-fuel ratio measuring device of the present invention, a low-pass filter having a time constant larger than the response time of the analyzer is interposed between the analyzer and the calculator. Therefore, the error factor caused by the difference in response time of the analyzer can be eliminated, which has the advantage of allowing highly accurate air-fuel ratio measurement.

[Brief explanation of the drawing]

The figure shows an air-fuel ratio measuring device as an embodiment of the present invention. In order to explain its operation, FIG. 1 shows the respective contents of carbon monoxide and carbon dioxide contained in engine exhaust gas. Figure 2 is a graph showing the relationship between the air-fuel ratio and the content of hydrocarbons contained in engine exhaust gas to explain its effect. Figure 3 is the electrical circuit. 4 and 5 are schematic diagrams showing the analyzer, and FIGS. 6a and 6b are waveform diagrams for explaining its operation. 1...Analyzer, 1a...Infrared emitter, 1b...Chopper, 1c...Optical filter, 1e...Gas filling chamber,
1f, 1'f...Sensor, 2...Analyzer, 2a...Hydrogen flame, 2b...Pipe line, 2c...Sensor, 3...Low pass filter, 4...Buffer amplifier, 5...Amplifier, 6...
Divider, 7... Addition amplifier, 8... Potentiometer, 9... Adder, 10... Potentiometer, AO
...Analog computing unit.

Claims (1)

[Claims] 1. An analyzer that analyzes each of carbon monoxide, carbon dioxide, and hydrocarbons contained in exhaust gas to detect each content, and a calculator that can calculate the air-fuel ratio based on the detection signal from the analyzer. An air-fuel ratio measuring device, comprising: a low-pass filter having a time constant larger than the response time of the analyzer, interposed between the analyzer and the calculator.