Abstract:
In order to provide an exhaust gas measurement apparatus having a simpler configuration capable measuring a concentration of a predetermined component contained in exhaust gas under various situations without deteriorating a measurement accuracy, there is provided a sampling mechanism that can select any one of two states, i.e., a first operation mode for outputting the sampled exhaust gas without dilution and a second operation mode for outputting the sampling exhaust gas mixed with dilution gas. In a situation where the sampling mechanism is operating in the first operation mode, in the case where the concentration of the predetermined component measured by a measurement apparatus body exceeds a predetermined first threshold value, the sampling mechanism is controlled such that the first operation mode thereof is changed to the second operation mode.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to JP Application No. 2015-241542, filed Dec. 10, 2015, the disclosure of which is incorporated in its entirety by reference herein. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an exhaust gas measurement apparatus and the like for measuring a concentration of such as a CO component (also, simply referred to as “CO concentration” hereinafter) contained in exhaust gas discharged from an internal combustion engine and the like. 
       BACKGROUND ART 
       [0003]    In this type of the exhaust gas measurement apparatus, as disclosed in Patent Literature 1, concentrations of various components contained in the exhaust gas discharged from an internal combustion engine are measured. 
         [0004]    Especially, a CO concentration is varied largely in a short time in a range from a several ppm order to a percentage (%) order according to an operating condition of an engine and a warming-up state of a catalyst. 
         [0005]    For example, in a state that a large amount of fuel is supplied and a catalyst is not yet sufficiently warmed, at a time of initial operation of the engine or the like, since there occurs an incomplete combustion and a catalytic function is not sufficiently exerted, CO gas produced by such as an incomplete combustion is discharged from a vehicle tailpipe of a vehicle without being oxidized to be CO 2  by the catalyst. Therefore, the CO concentration at this time is extremely high. Meanwhile, in the case where the catalyst is warmed up, the CO component is almost oxidized to be CO 2  by the catalyst and therefore the concentration of the CO component contained in the exhaust gas is reduced to be a few ppm order. 
         [0006]    In this way, since a difference between a high concentration and a lower concentration of the CO component is large, the CO concentration has been conventionally measured by providing two types of CO concentration meters having, for example, different measurement ranges. 
         [0007]    However, since it is necessary to use two types of the CO concentration meters, there is a problem that a maintenance cost and an initial investment cost are increased. Further, also in measurement accuracy, a correlation at a timing of switching between the two CO concentration meters becomes a problem of measurement accuracy in some cases. 
         [0008]    Similar problems may also arise in measuring concentrations of the other components (for example, THC and the like) contained in the exhaust gas. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: JP2014-174055A 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    Therefore, the present invention has been made in consideration of the above problems, and an essential object thereof is to provide an exhaust gas measurement apparatus capable of measuring a concentration of a predetermined component contained in exhaust gas under various situations with a simpler configuration without deteriorating a measurement accuracy. 
       Solution to Problem 
       [0011]    That is, in one aspect of the present invention, an exhaust gas measurement apparatus is characterized by comprising following components (1) to (3): 
         [0012]    (1) a sampling mechanism adapted to sample exhaust gas discharged from an internal combustion engine and to be able to select any one of two states of a first operation mode and a second operation mode, specifically, in the first operation mode, the sampled exhaust gas being outputted without dilution or the sampled exhaust gas mixed with dilution gas of a predetermined ratio or less being outputted, and in the second operation mode, the sampling exhaust gas mixed with dilution gas beyond a predetermined ratio being outputted; 
         [0013]    (2) a measurement apparatus body adapted to introduce the gas outputted from the sampling mechanism and adapted to measure a concentration of a predetermined component contained in the gas; and 
         [0014]    (3) a control mechanism adapted to control the sampling mechanism, and in the case where the concentration measured by the measurement apparatus body exceeds a predetermined first threshold value in a situation that the sampling mechanism is operating in the first operation mode, the control mechanism being adapted to control the sampling mechanism so as to change the first operation mode to the second operation mode. 
         [0015]    With this configuration, even if there may be a case where a concentration of a predetermined component contained in the sampling exhaust gas is increased due to such as a change of the state of the internal combustion engine and exceeds a measurable range of the measurement apparatus body and, for example, it will be unmeasurable directly, by switching the operation mode of the sampling mechanism to the second operation mode, the sampling exhaust gas is diluted and the concentration of the predetermined component can be decreased to a measurable concentration range of the measurement apparatus body. Thus, the concentration of the predetermined component can be measured by a single measurement apparatus body. It is needless to say that, in the case of diluting the sampling exhaust gas, it is necessary to calculate the concentration of the predetermined component contained in the exhaust gas in consideration of a dilution ratio to the measurement concentration obtained by the measurement apparatus body. However, since it is not necessary to provide a plurality of types of measurement apparatus main bodies (for example, a CO concentration meter) having different measurable ranges as is required in the conventional case, the configuration of the exhaust gas measurement apparatus can be simplified. Moreover, there is no correlation problem which has been caused due to switching of a plurality of measurement apparatus main bodies as in the conventional case, and not only the measurement accuracy can be ensured but also it becomes possible to contribute to improvement of the measurement accuracy. 
         [0016]    In order to be able to deal with also in the case where the concentration of the predetermined component contained in the sampling exhaust gas is decreased from a high state, it is preferable that the control mechanism is configured as follows. 
         [0017]    In other words, it is preferable that, in the case where the concentration measured by the measurement apparatus body is below a predetermined second threshold value in a situation that the sampling mechanism is operating in the second operation mode, the control mechanism is adapted to control the sampling mechanism so as to change the second operation mode to the first operation mode. 
         [0018]    As a specific embodiment, in the second operation mode, it is sufficient to allow the dilution gas to be added and mixed to the sampling exhaust gas flowing in the first operation mode. However, in this configuration, the flow rate of the gas to be introduced to the measurement apparatus body in the second operation mode becomes larger by a dilution gas amount, compared to that in the first operation mode. Therefore, there may arise a significant difference between the flow rates of the gas introduced to the measurement apparatus body in the first operation mode and in the second operation mode, and it is liable to cause a measurement error due to the above fact. 
         [0019]    Therefore, in order to reduce the difference between the flow rates of the gas introduced to the measurement apparatus body in the first operation mode and in the second operation mode and relieve the above problem, it is preferred that, the flow rates of the sampling exhaust gas to be introduced to the measurement apparatus body are set to be different from each other between in the first operation mode and in the second operation mode, and the flow rate of the sampling exhaust gas in the first operation mode is set to be larger than that in the second operation mode. 
       Advantageous Effects of Invention 
       [0020]    According to the exhaust gas measurement apparatus according to the present invention, since the concentration of the predetermined component can be measured by a single measurement apparatus body even in the case where the concentration of the predetermined component contained in the exhaust gas is largely changed, the configuration of the exhaust gas measurement apparatus can be simplified and further it becomes possible to ensure the measurement accuracy. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a fluid circuit diagram showing an entire exhaust gas measurement apparatus in a first embodiment of the present embodiment; 
           [0022]      FIG. 2  is a fluid circuit diagram showing a flow of gas in a first operation mode of the exhaust gas measurement apparatus in the same embodiment; 
           [0023]      FIG. 3  is a fluid circuit diagram showing a flow of the gas in a second operation mode of the exhaust gas measurement apparatus in the same embodiment; 
           [0024]      FIG. 4  is a fluid circuit diagram showing a flow of the gas in a first calibration mode of the exhaust gas measurement apparatus in the same embodiment; 
           [0025]      FIG. 5  is a fluid circuit diagram showing a flow of the gas in a second calibration mode of the exhaust gas measurement apparatus in the same embodiment; 
           [0026]      FIG. 6  is a fluid circuit diagram showing an entire exhaust gas measurement apparatus in a second embodiment of the present embodiment; and 
           [0027]      FIG. 7  is a fluid circuit diagram showing an entire exhaust gas measurement apparatus in the other embodiment of the present embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0028]    The following describes various embodiments of the present invention referring to the accompanying drawings. 
       First Embodiment 
       [0029]    As shown in  FIG. 1 , an exhaust gas measurement apparatus  100  according to the present embodiment includes: a sampling mechanism  1  for sampling a partial portion of exhaust gas discharged from an internal combustion engine (not shown); a measurement apparatus body  2  which is connected to the sampling mechanism  1  and measures a concentration of a predetermined component (CO in this case) contained in the gas outputted from the sampling mechanism  1 ; and a control mechanism  3  for controlling the sampling mechanism  1 . Each part is described as below. 
         [0030]    The sampling mechanism  1  is adapted to be able to select any one of two operation modes: a first operation mode in which an internal flow channel thereof is switched and the sampled exhaust gas (also, referred to as “sampling exhaust gas” hereinafter) is outputted directly; and a second operation mode in which the sampling exhaust gas is mixed with a predetermined ratio of dilution gas and the resultant mixture gas is outputted. Note that the sampling exhaust gas mentioned here may be raw gas outputted from the internal combustion engine or diluted exhaust gas diluted by such as dilution tunnel CVS. The following describes more specifically. 
         [0031]    The sampling mechanism  1  includes a first flow channel system  11  in which the sampling exhaust gas flows in the first operation mode and a second flow channel system  12  in which the sampling exhaust gas flows in the second operation mode. 
         [0032]    The first flow channel system  11  includes a first exhaust gas flow channel  11   a  to which the sampling exhaust gas is introduced. The first exhaust gas flow channel  11   a  is provided with a first exhaust gas introduction port  11   b  at its starting end which is, for example, connected to an external pump P. As shown in  FIG. 1 , the first exhaust gas flow channel  11   a  is adapted to sample the exhaust gas sucked by the external pump P and guide the sampling exhaust gas directly to the measurement apparatus body  2  which is connected to a terminal end of the first exhaust gas flow channel  11   a.  In  FIG. 1 , reference numeral V 1  provided at a starting end portion of the first exhaust gas flow channel  11   a  denotes a first valve for opening and closing the first exhaust gas flow channel  11   a.    
         [0033]    The second flow channel system  12  includes: a second exhaust gas flow channel  12   a  to which the sampling gas is introduced; a dilution gas flow channel  12   b  to which the dilution gas (for example, N2) is introduced; and a dilution portion  12   c  which is adapted to mix the sampling exhaust gas flowing through the second exhaust gas flow channel  12   a  and the dilution gas flowing through the dilution gas flow channel  12   b  at a predetermined constant ratio and guide the resultant mixture gas to the measurement apparatus body  2 . 
         [0034]    The second exhaust gas flow channel  12   a  is provided with a second exhaust gas introduction port  12   d  at its starting end which is connected to the external pump. As shown in  FIG. 1 , the second exhaust gas flow channel  12   a  is adapted to sample the exhaust gas sucked by the external pump P. In  FIG. 1 , reference numeral V 2  provided at a starting end portion of the second exhaust gas flow channel  12   a  denotes a second valve for opening and closing the second exhaust gas flow channel  12   a.    
         [0035]    The dilution gas flow channel  12   b  is provided with a dilution gas introduction port  12   e  at its starting end which is, for example, connected to a dilution gas source such as a gas bomb (not shown) and adapted to introduce the dilution gas supplied from the dilution gas source. In  FIG. 1 , reference numeral V 3  provided at a starting end portion of the dilution gas flow channel  12   b  denotes a third valve for opening and closing the dilution gas flow channel  12   b.    
         [0036]    The dilution portion  12   c  includes: an exhaust gas acquisition part  121  and a dilution gas acquisition part  122  for acquiring the sampling exhaust gas flowing through the second exhaust gas flow channel  12   a  and the dilution gas flowing through the dilution gas flow channel  12   b , respectively, so as to be at the predetermined constant ratio therebetween; and a mixing part  123  for mixing the exhaust gas and the dilution gas outputted from the exhaust gas acquisition part  121  and the dilution gas acquisition part  122 , respectively. 
         [0037]    The exhaust gas acquisition part  121  includes: a first pressure regulating valve R 1  connected to the second exhaust gas flow channel  12   a ; and a first fluid resistance element C 1  such as a capillary connected to a downstream side of the first pressure regulating valve R 1  in the second exhaust gas flow channel  12   a . The first pressure regulating valve R 1  is adapted to keep the internal pressure of the second exhaust gas flow channel  12   a  to be a predetermined constant pressure by discharging a partial portion of the sampling exhaust gas from an escape port thereof. The first fluid resistance element C 1  is adapted to keep the flow rate of the exhaust gas flowing through the first fluid resistance element C 1 , i.e., the flow rate of the sampling exhaust gas outputted from the exhaust gas acquisition part  121  to be a predetermined constant value by connecting the first fluid resistance element C 1  to the second exhaust gas flow channel  12   a  kept at the predetermined constant pressure. 
         [0038]    The dilution gas acquisition part  122  includes: a second pressure regulating valve R 2  having an input port connected to the terminal end of the dilution gas flow channel  12   b ; and a second fluid resistance element C 2  such as a capillary connected to an output port of the second pressure regulating valve R 2 . The second pressure regulating valve R 2  is adapted to keep the output port thereof to be at a predetermined constant pressure by discharging a partial portion of the dilution gas from an escape port thereof. The second fluid resistance element C 2  is adapted to keep the flow rate of the dilution gas flowing through the second fluid resistance element C 2 , i.e., the flow rate of the dilution gas outputted from the dilution gas acquisition part  122  to be a predetermined constant value by connecting the second fluid resistance element C 2  to the output port kept at the predetermined constant pressure. 
         [0039]    The mixing part  123  is adapted to introduce the sampling exhaust gas and the dilution gas respectively outputted from the exhaust gas acquisition part  121  and the dilution gas acquisition part  122  at a constant ratio and at a constant flow rate and mix these outputted sampling exhaust gas and dilution gas and then guide the resultant mixture gas to the measurement apparatus body  2 . Here, a pipe member commonly connected to the output ports of the exhaust gas acquisition part  121  and the dilution gas acquisition part  122  plays the function thereof. 
         [0040]    In this embodiment, the ratio of the sampling exhaust gas and the dilution gas in the mixture gas that is outputted from the second flow channel system  12  is approximately 1:19. This dilution ratio (about 20 times) is determined by a measurement dynamic range (a ratio of the measurement maximum value to the measurement minimum value) and a resolution of the measurement apparatus body  2 . In specific, the dilution ratio is set to be in a degree of 1/5 to 1/500, preferably 1/10 to 1/100 of the dynamic range. Meanwhile, the flow rate of the mixture gas is set to be substantially equal to the flow rate of the sampling exhaust gas outputted from the first flow channel system  11 . 
         [0041]    The measurement apparatus body  2  is, for example, absorption photometer typed one, and, although not shown, it is adapted to guide light emitted from a light source to a light-transmission cell while being filled with a measurement target gas and then calculate a concentration of a CO component contained in the measurement target gas from an absorbance of a predetermined wavelength of the light. The measurement range of the measurement apparatus body  2  is determined by an optical path of the cell, and since the CO concentration is low according to improvement of recent catalyst performance, the measurement apparatus body  2  having a long cell length and low concentration measurement range is used. Note that the measurement apparatus body  2  is not limited to absorption photometer typed one. 
         [0042]    The control mechanism  3  is an electric circuit including, such as a CPU, a memory, an A/D converter, a D/A converter, and an amplifier (not shown), and it is configured that the CPU and the peripheral equipment thereof cooperate according to a program stored in the memory, and thus the control mechanism  3  controls the sampling mechanism  1  and performs a switching operation of the operation mode thereof. 
         [0043]    Specifically, in the case where the sampling mechanism  1  is set in the first operation mode, the control mechanism  3  transmits an opening/closing signal to the sampling mechanism  1  to open the first valve V 1  and simultaneously close the second valve V 2  and the third valve V 3 . Alternatively, instead of closing the second valve V 2  and the third valve V 3 , a fourth valve V 4  provided on the pipe connecting between the mixing part  123  and the measurement apparatus body  2  may be closed. By this arrangement, as shown in  FIG. 2 , the sampling exhaust gas can be guided to the measurement apparatus body  2  without being diluted through the first flow channel system  11 . 
         [0044]    Meanwhile, in the case where the sampling mechanism  1  is set in the second operation mode, the control mechanism  3  transmits an opening/closing signal to the sampling mechanism  1  to open the second valve V 2  and third valve V 3  (together with the fourth valve  4 ) and simultaneously close the first valve V 1 . By this arrangement, as shown in  FIG. 3 , the sampling exhaust gas is guided to the second flow channel system  12  and diluted, and thus the diluted exhaust gas is guided to the measurement apparatus body  2 . Next, the following describes a switching timing of the operation mode. 
         [0045]    In the initial state, the sampling mechanism  1  is in the first operation mode. In this state, as shown in  FIG. 2 , undiluted sampling exhaust gas is guided to the measurement apparatus body  2  and the CO concentration is measured. 
         [0046]    The control mechanism  3  receives the measurement data of the CO concentration transmitted from the measurement apparatus body  2  and monitors the value thereof 
         [0047]    Then in this first operation mode, for example, in the case where the concentration of the CO component contained in the sampling exhaust gas exceeds predetermined first threshold value such as in a state that the catalyst is not sufficiently warmed before the warming-up is completed, the control mechanism  3  switches the sampling mechanism  1  to be in the second operation mode. As a result, as shown in  FIG. 3 , the diluted sampling exhaust gas (i.e., mixture gas) is guided to the measurement apparatus body  2  and the concentration of the CO component contained in the mixture gas is measured. Note that the first threshold value is set to the measurable maximum value of the measurement apparatus body  2  or a value slightly smaller than the measurable maximum value. 
         [0048]    Meanwhile, when the sampling mechanism  1  is in the state of the second operation mode, in the case where the catalyst warms up and the like and the function thereof is exerted, the concentration of the CO component contained in the sampling exhaust gas is lowered. Subsequently, when the concentration of the CO component contained in the mixture gas is lowered below a predetermined second threshold value, the control mechanism  3  switches the mode of the sampling mechanism  1  to the first operation mode. As a result, the undiluted sampling exhaust gas is guided to the measurement apparatus body  2  and the concentration of the CO component contained in the sampling exhaust gas is measured. 
         [0049]    The second threshold value is set to measurable minimum value of the measurement apparatus body  2  or a slightly larger than the measurable minimum value. 
         [0050]    In addition, in this embodiment, the sampling mechanism  1  is configured to be able to select a first calibration mode and a second calibration mode in addition to the first operation mode and second operation mode. 
         [0051]    In the first calibration mode, it is possible to calibrate the measurement concentration obtained in the first operation mode. For this purpose, a first calibration gas flow channel  41  for guiding calibration gas of a predetermined low CO concentration is connected to the middle of the first exhaust gas flow channel  11   a  and a fifth valve V 5  is provided in the middle of the first calibration gas flow channel  41 . 
         [0052]    In this first calibration mode, it is intended that, according to a command from the control mechanism  3 , while the first valve V 1  is closed, the fifth valve V 5  is opened, and thus the low concentration calibration gas instead of the sampling exhaust gas is guided to the first exhaust gas flow channel  11   a.  The other operation is the same as that in the first operation mode. 
         [0053]    Thus, it is intended that the low concentration calibration gas is introduced to the measurement apparatus body  2  and the measurement apparatus body  2  can be calibrated. 
         [0054]    In the second calibration mode, it is possible to calibrate the measurement concentration obtained in the second operation mode. For this purpose, a second calibration gas flow channel  42  for guiding calibration gas of a predetermined high CO concentration is connected to the middle of the second exhaust gas flow channel  12   a  and a sixth valve V 6  is provided in the middle of the second calibration gas flow channel  42 . 
         [0055]    In this second calibration mode, it is intended that, according to a command from the control mechanism  3 , while the second valve V 2  is closed, the sixth valve V 6  is opened, and thus, as shown in  FIG. 5 , the high concentration calibration gas instead of the sampling exhaust gas is supplied to the second exhaust gas flow channel  12   a . The other operation is the same as that in the second operation mode. 
         [0056]    Thus, it is intended that the high concentration calibration gas is introduced to the measurement apparatus body  2  and the measurement apparatus body  2  can be calibrated. 
       Second Embodiment 
       [0057]    In the first embodiment, although the flow channel systems are separated for the sampling exhaust gas to pass through in the first operation mode and in the second operation mode, respectively, it is also possible that, in the second operation mode, the dilution gas may be added and mixed to the sampling exhaust gas flowing in the first operation mode. 
         [0058]    That is, as shown in  FIG. 6 , the exhaust gas measurement apparatus  100  according to the second embodiment is provided with a first exhaust gas flow channel  51  for introducing the sampling exhaust gas to the measurement apparatus body  2  and a dilution gas flow channel  52  which is connected to the middle of the first exhaust gas flow channel  51 . Thus, in the first operation mode, according to a command from the control mechanism  3 , while a valve  11  provided on the first exhaust gas flow channel  51  is opened, a valve V 12  provided on the dilution gas flow channel  52  is closed, such that only the sampling exhaust gas is allowed to be guided to the measurement apparatus body  2 . Meanwhile, in the second operation mode, the valve V 12  provided on the dilution gas flow channel  52  is opened and mixture gas obtained by mixing the sampling exhaust gas and the dilution gas is allowed to be guided to the measurement apparatus body  2 . 
         [0059]    However, in this case, the flow rate of the gas guided to the measurement apparatus body  2  in the second operation mode becomes larger than that in the first operation mode only by an amount of the dilution gas, and there arises a significant difference in flow rate in the gas introduced to the measurement apparatus body  2  between in the first operation mode and in the second operation mode. Therefore, there may arise a difference in internal pressure of the cell and in subsequent back pressure thereafter, and it is liable cause a measurement error due to this difference. Conversely, in the first embodiment, since there is no significant difference in the flow rates of the gas introduced to the measurement apparatus body  2  either in the first operation mode or in the second operation mode, there is a merit that a malfunction such as a measurement error due to such a difference is hardly caused. 
         [0060]    Further, in the exhaust gas measurement apparatus according to each of the first and second embodiments, the flow rates of the gas guided to the measurement apparatus body  2  are different and flow rate lengths to the measurement apparatus body  2  are different between in the first operation mode and in the second operation mode, there may possibly arise a difference in response time of the measurement apparatus body  2  when switching between the first operation mode and the second operation mode. As a method of making these response times coincident, the exhaust gas measurement apparatus may be configured that, a movement average time used for calculating measurement concentration is reduced to accelerate the response time for a mode of a slower response time when switching between the first operation mode and the second operation mode, or a waiting time is differently set according to a selected operation mode. Note that the present invention is not limited to the above embodiments. 
         [0061]    Although the undiluted exhaust gas is guided to the measurement apparatus body in the first operation mode, the exhaust gas diluted at a dilution ratio lower than that in the second operation mode may be also guided to the measurement apparatus body. 
         [0062]    In the first embodiment, gas is allowed to selectively flow only in one of the first flow channel system  11  or the second flow channel system  12 . However, it may be also possible that, as shown in  FIG. 7 , while gas is allowed to simultaneously flow in the first flow channel system  11  (more specifically, in the first exhaust gas flow channel  11   a ) and in the second flow channel system  12  (more specifically, in the mixing part  123 ), either one of the gases flowing in the first and second flow channel systems  11  and  12  can be guided to the measurement apparatus body  2  and the other one of the gases is discharged to the outside of the exhaust gas measurement apparatus  100  immediately before the measurement apparatus body  2 . 
         [0063]    Therefore, the exhaust gas measurement apparatus  100  shown in  FIG. 7  is configured to further include a first delivery channel  131  which is provided immediately before a junction to the mixing part  123  in the first exhaust gas flow channel  11   a,  and a second delivery channel  132  which is provided immediately before the fourth valve V 4  in the mixing part  123 . Note that, in  FIG. 7 , the members corresponding to those in the first embodiment are designated by the same reference signs. 
         [0064]    A switching valve  4  is provided on the first exhaust gas flow channel  11   a  (more specifically, in the downstream side of the first delivery channel  131  in the first exhaust gas flow channel  11   a ) and another switching valve  5  is provided on the first delivery channel  131 . Thus, by opening any one of the switching valves  4  and  5  while closing the other, the gas flowing in the first exhaust gas flow channel  11   a  is allowed to be switched whether the gas is discharged to the outside of the exhaust gas measurement apparatus  100  through the first delivery channel  131  or guided to the measurement apparatus body  2 . 
         [0065]    Meanwhile, further another switching valve  6  is provided on the second delivery channel  132 . Thus, by opening any one of the switching valve  6  or the fourth valve V 4  while closing the other, the gas flowing in the mixing part  123  is allowed to be switched whether the gas is discharged to the outside of the exhaust gas measurement apparatus  100  through the second delivery channel  132  or guided to the measurement apparatus body  2 . 
         [0066]    In this arrangement shown in  FIG. 7 , the first to third valves V 1  to V 3  are held in a normally opened state based on instructions from the control mechanism  3  in the operation mode. 
         [0067]    Thus, in the first operation mode, based on the instructions from the control mechanism  3 , by closing the switching valve  5  and opening the switching valve  4  while the fourth valve V 4  is closed and the switching valve  6  is opened to thereby escape the mixture gas from the second delivery channel  132 , the gas (exhaust gas) flowing in the first flow channel system  11  is allowed to be guided to the measurement apparatus body  2 . 
         [0068]    In the second operation mode, based on the instructions from the control mechanism  3 , by opening the fourth valve V 4  and closing the switching valve  6  while the switching valve  4  is closed and the switching valve  5  is opened to thereby escape the exhaust gas from the first delivery channel  131 , the gas (mixture gas) flowing in the second flow channel system  12  is allowed to be guided to the measurement apparatus body  2 . 
         [0069]    With this configuration as described above, in either case of the first operation mode or the second operation mode, a portion in which the flow of the gas stops in the first flow channel system  11  and the second flow channel system  12  can be shortened. Therefore, when switching between the first operation mode and the second operation mode, the time until the flow of the gas from the first flow channel system  11  or the second flow channel system  12  is stabilized can be reduced. 
         [0070]    In particular, in the second flow channel system  12 , it is advantageous since the dilution ratio of the exhaust gas and the dilution gas can be kept stable before and after switching the operation mode. 
         [0071]    In each of the embodiments, although the flow rate of the gas is constantly controlled using the pressure regulating valve and the fluid resistance element, the rates of the dilution gas and the sampling exhaust gas may be also controlled by a mass flow controller. Further, the dilution ratio may be also changed according to a type of an internal combustion engine or a testing condition. 
         [0072]    A third operation mode or more operation modes may be provided to be able to change the dilution ratio in three steps or more. 
         [0073]    In each of the embodiments, although the measurement concentration obtained in the first operation mode is calibrated according to the first calibration mode and the measurement concentration obtained in the second operation mode is calibrated according to the second calibration mode, it may be also possible to previously set a predetermined correlation coefficient between the measurement concentration in the first operation mode and the measurement concentration in the second operation mode to thereby calibrate the measurement concentration according to any one of the first and second calibration mode. Thus, it is also possible to calibrate the measurement concentration regarding the other operation mode using the correlation coefficient. 
         [0074]    In this case, the correlation coefficient is to be stored in a predetermined region of the memory, and as an aspect of the correlation function, a numerical expression format or a table format may be also used. 
         [0075]    Further, the low concentration calibration gas and the high concentration calibration gas may be supplied from separately prepared bombs, respectively, or only the high concentration calibration gas is prepared and the low concentration calibration gas may be adjusted by diluting the high concentration calibration gas. 
         [0076]    In addition, various modifications and combinations of the components in the embodiments can be made without departing from the spirit of the present invention. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  . . . Exhaust gas measurement apparatus 
         . . . Sampling mechanism 
         . . . Measurement apparatus body 
         . . . Control mechanism