In a low-pressure testing apparatus for analyzing gas exhausted from cars under a condition in which air pressure is low, an exhaust-gas analyzing device is provided with a dilution tunnel for diluting exhaust gas from cars with air which is under a decompressed condition, the exhaust-gas analyzer is connected to said dilution tunnel at a supply port side thereof and arranged in a low-pressure testing room, and an exhaust intake is open to the air outside of the low-pressure testing room via airtight piping. An influence caused by the fluctuation of pressure within the low-pressure testing room upon the accuracy of anaylsis can be eliminated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an analyzing device for analyzing gas 
exhausted from cars. 
2. Description of the Prior Art 
In order to reduce a distance (l in FIG. 3) from a sample-inlet of a 
dilution tunnel 6 for diluting exhaust gas from cars with air which is in 
a decompressed condition, that is to say air within a low-pressure testing 
room, to an exhaust-gas analyzer 8, the exhaust-gas analyzer has been 
arranged in the low-pressure testing room. That is to say, a construction 
as shown in FIG. 3 has been used. Referring to FIG. 3, reference numeral 1 
designates a low-pressure testing room, reference numeral 2 designates 
atmosphere pressure, reference numeral 3 designates a decompression 
blower, reference numeral 4 designates a car, reference numeral 5 
designates a chassis dynamometer, reference numeral 6 designates a 
dilution tunnel, reference numeral 7 designates air, reference numeral 8 
designates an analyzer, reference numeral 9 designates an overflow line, 
reference numeral 10 designates a zero gas passage, reference numeral 11 
designates a span gas passage, reference numeral 12 designates a bag 
sample passage, and reference numeral 13 designates a valve. 
When HC (hydrocarbon) is measured, if the temperature is reduced, certain 
kinds of HC do not assume a gaseous state, so that it is necessary to 
maintain the temperature high and therefore, l has been reduced. For 
example, such is the case when an HC analyzer is used as an exhaust-gas 
analyzer. 
An exhaust-gas analyzer for use with a car is influenced with respect to 
its analytical sensitivity by a fluctuation in atmospheric pressure. 
Although the accuracy of the exhaust-gas analysis is not influenced by the 
fluctuation of atmospheric pressure in nature at the same altitude, if 
atmospheric pressure is reduced to about a half atm. as occurs in the 
low-pressure testing room, for example, the pressure of air is reduced to 
460 to 400 mmHg, as a result, the accuracy of the exhaust-gas analysis is 
diminished. The conventional analyzer has not taken measures for solving 
the above-described problem. Therefore, according to the known method, the 
measurement is carried out under a condition in which the accuracy is 
reduced in dependence upon a degree of the setting of pressure in the 
low-pressure testing room, or, in which pressure is calibrated (this is 
not easy) and then data is read. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an exhaust-gas 
analyzing device capable of reducing an influence caused by the 
fluctuation of atmospheric pressure within a low-pressure testing room 
upon the accuracy of the analyzer in view of the above-described problems 
of the prior art. An exhaust-gas analyzing device in a low-pressure 
testing apparatus for analyzing gas exhausted from cars under a condition 
in which the pressure of air is low,according to the present invention,is 
characterized in the provision of a dilution tunnel for diluting exhaust 
gas from cars with air which is in a decompressed condition, an 
exhaust-gas analyzer connected with said dilution tunnel at a supply port 
side thereof and arranged in said low-pressure testing room, and an 
exhaust intake open to the air outside of the low-pressure testing room 
via airtight piping. 
Accordingly, since the accuracy of the analyzer is the same as when the 
analyzer is arranged under an atmospheric condition in which the 
sample-exhausting system of the analyzer is arranged in the outside air, 
an influence caused by the fluctuation of atmospheric pressure within the 
low-pressure testing room upon the accuracy of the analyzer is reduced by 
placing the exhaust pipe in open communication with the air in an airtight 
manner and by providing a pressure pump in the sample-supply system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments according to the present invention will be 
described below with reference to the drawings. 
FIG. 1 is a diagram showing an apparatus according to one preferred 
embodiment of the present invention. 
Referring to FIG. 1, reference numerals 1, 2, 4 to 13 designate the same 
members as in FIG. 3 showing the conventional apparatus. 
Reference numeral 14 designates an opening at an air side of an 
exhaust-pipe 16 connected to the analyzer and reference numeral 15 
designates a pressure pump provided in the sample-supply system. In 
addition, reference numeral 17 designates nearly 1 atm. 
The operation of the above-described apparatus is described below. 
According to the present invention, since the sensitivity of the analyzer 8 
is under the same condition as if the analyzer 8 was disposed under an 
atmospheric pressure, an influence caused by the fluctuation of pressure 
within the low-pressure testing room upon the accuracy of the analyzer 8 
is reduced by placing the exhaust pipe in open communication with outside 
air in an airtight manner and by providing the pressure pump 15 in the 
sample-supply system. 
FIG. 2 is a diagram showing an apparatus according to another preferred 
embodiment of the present invention. 
The apparatus of FIG. 2 is different from the apparatus of FIG. 1 merely in 
that the pressure pump 15 is included in an analyzing portion 18. The 
operation and effects are the same. 
The present invention exhibits the following effect. 
An influence caused by the fluctuation of pressure within the low-pressure 
testing room upon the accuracy of analysis can be eliminated.