JP3968085B2 - Partial dilution type gas dilution system for measuring exhaust gas and partial dilution type gas dilution system for measuring particulate matter in exhaust gas - Google Patents

Description

  The present invention relates to a partial dilution type exhaust gas measurement gas dilution system in which a part of exhaust gas from an engine or the like is diluted with a dilution gas such as air, and particulates in the partial dilution type exhaust gas. The present invention relates to a gas dilution system for measuring substances.

  As a gas dilution system necessary for the measurement of particulate matter (abbreviated as PM) contained in gas discharged from automobile diesel engines, etc., in recent years, all exhaust gas has been collected and used as a whole. In place of the conventional full dilution system for dilution, a small dilution system of a partial dilution system that performs flow rate control and partial sampling of exhaust gas has been adopted. This partial dilution type gas dilution system by partial sampling controls the flow rate of the dilution gas (for example, air) for diluting the exhaust gas while maintaining the exhaust gas after dilution at a constant flow rate. This is a system for controlling the sampling flow rate of exhaust gas obtained as the difference in flow rate.

  FIG. 5 shows an example of a partial dilution type gas dilution system by partial sampling. In this figure, 1 is a diesel engine mounted on an automobile, for example, and 2 is an exhaust pipe connected thereto. A probe 3 is inserted and connected to the exhaust pipe 2 for sampling the exhaust gas G flowing through the exhaust pipe 2, and its downstream side is connected to a dilution tunnel 4 for diluting the exhaust gas G that has been sampled. Reference numeral 5 denotes a supply path for dilution air A connected to the upstream side of the dilution tunnel 4, and a dilution gas flow rate control device 6 as shown in FIG. 6 is provided.

  That is, in FIG. 6, reference numeral 7 denotes a roots blower pump provided in the flow path 8 and capable of changing the suction capacity by, for example, rotational speed control, and is controlled by the inverter (frequency converter) 9. Reference numeral 10 denotes a venturi flow meter as a differential pressure flow meter with high measurement accuracy. A pressure sensor 11, a differential pressure sensor 12 and a temperature sensor 13 for detecting the pressure of air flowing through the flow path 8 are provided in the vicinity thereof. Reference numeral 14 denotes a flow rate calculation unit that calculates the flow rate (actual flow rate) of the air A flowing through the flow path 8 based on the detection outputs of the sensors 10 to 13. A comparison control circuit 15 compares the actual flow rate of air obtained in the flow rate calculation unit with a preset flow rate and outputs a predetermined control signal to the inverter 9.

  Reference numeral 16 denotes a gas flow path that is connected to the downstream side of the dilution tunnel 4 and through which the diluted sample gas S flows. The downstream side of the flow path 16 branches into two flow paths 17 and 18. 18 are provided with filters 19 and 20 for collecting PM contained in the sample gas, and control valves 21 and 22 that can change the throttle amount (pressure loss). The other gas flow path 18 is configured as a bypass gas flow path for flowing the exhaust gas at the time of non-steady state.

  Reference numeral 23 denotes a three-way solenoid valve as a flow path switching means provided on the downstream side of the sample gas flow path 17 and the bypass flow path 18. The port 23a is connected to the sample gas flow path 17 and the port 23b is connected to the bypass flow path 18. In addition to being connected, the port 23 c is connected to a gas flow path 24 on the downstream side of the three-way solenoid valve 23.

  The gas flow path 24 is provided with a suction pump capable of changing the suction capacity by controlling the rotation speed, for example, a roots blower pump 25, and a differential pressure flow meter with high measurement accuracy, for example, a venturi flow meter 26, in this order. ing. Reference numeral 27 denotes a pressure sensor for detecting the pressure of the gas flowing through the gas flow path 24, reference numeral 28 denotes a differential pressure sensor, and reference numeral 29 denotes a temperature sensor.

  Reference numeral 30 denotes an inverter (frequency converter) that controls the Roots blower pump 25, and reference numeral 31 denotes a flow rate control unit that controls the entire apparatus. The flow rate control unit 31 outputs commands to the control valves 21 and 22 and the inverter 30 and receives detection outputs from the sensors 27 to 29.

  Thus, in the gas sample system, a command value is output to the inverter 9 from the comparison control circuit 15 in the dilution gas flow control device 6, and the roots blower pump 7 provided in the flow path 8 is controlled based on this command value. As a result, dilution air having a predetermined flow rate is supplied to the dilution tunnel 4, while a command value output by a PID controller (not shown) provided in the flow rate control unit 31 is output to the inverter 30. Based on the command value output from the inverter 30 based on this command, the Roots blower pump 25 is controlled so that the sample gas flow rate S flowing through the gas flow paths 16, 18, and 24 is always controlled to a predetermined flow rate. Thereby, the sampling flow rate of the exhaust gas is controlled.

  However, in the conventional dilution gas flow rate control device 6 having the above-described configuration, the pump 7 and the venturi flow meter 10 are provided in series with each other. In other words, the venturi flow meter 10 as the air flow rate measuring means has a high flow rate measurement accuracy of about ± 0.1 to 0.2% in the flow rate region near the full scale. The pump 7 as the control means changes the flow rate by its rotation, and the flow control response speed has a limit of about 0.5 seconds to 1 second due to the inertia inherent in the pump.

  However, in the above-described dilution gas flow rate control device 6, even if the pump 7 is replaced with a piezo valve and a pressurized air source on the upstream side, and the high-speed response characteristic of the piezo valve is used, it is relatively large. In order to control the flow rate, the piezo valve becomes large, or the internal orifice of the piezo valve becomes large in diameter, resulting in a delay in response, and in any case of the combination of the venturi flow meter 10 and the pump. Control delay will occur. For this reason, there was a stagnation lacking in high-speed response and high accuracy of flow rate control necessary for transient measurement of engine exhaust gas.

  In addition, the dilution gas flow rate control device 6 has the following problems. That is, in order to control the sampling flow rate of the exhaust gas G from the engine 1, it is necessary to control the flow rate of the dilution air A. In this case, however, the flow rate of the dilution air A is controlled from zero to the maximum flow rate. In practice, the flow rate may be controlled in a flow rate region of about 70% to 100% of the maximum flow rate of the dilution air A. That is, the maximum flow rate of the dilution air A from the maximum flow rate to about 70% is always constant, and the variable portion in the range from 70% to the maximum flow rate may be controlled. In the gas flow rate control device 6, since the flow rate of the dilution air A was controlled from zero to the maximum flow rate, the high-speed response was lacking.

  The present invention has been made in consideration of the above-mentioned matters, and the purpose thereof is a dilution used in a partial dilution method by so-called partial sampling in which a part of exhaust gas from an engine is diluted with a dilution gas such as air. An object of the present invention is to provide a dilution gas flow rate control device capable of controlling a working gas at a high speed response and high accuracy while having a relatively large flow rate.

  In order to achieve the above object, a gas dilution system for exhaust gas measurement of a partial dilution system according to the present invention comprises a dilution tunnel for diluting a partially collected exhaust gas, and a dilution gas supply connected to the upstream side of the dilution tunnel. A gas flow path connected to the downstream side of the dilution tunnel and through which the diluted sample gas flows, the dilution gas supply path and the gas flow path each including a differential pressure flow meter, and The dilution gas supply path is provided with a first flow path for flowing a constant flow of dilution gas and a second flow path provided with a piezo valve for controlling the flow of the dilution gas in parallel. A differential pressure flow meter included in the working gas supply path is provided in a third flow path provided downstream from a confluence of the first flow path and the second flow path, and the piezo valve Included in gas supply path In which opening adjustment is performed based on the actual flow rate of the diluent gas detected by that differential pressure flow meter.

  In another aspect, the present invention provides a gas dilution system for measuring particulate matter contained in exhaust gas discharged from an engine or the like, the dilution tunnel for diluting a partially collected exhaust gas, and the dilution tunnel A dilution gas supply path connected to the upstream side of the tunnel, a gas flow path connected to the downstream side of the dilution tunnel and through which the diluted sample gas flows, and particulate matter contained in the sample gas are collected A filter is provided in the gas flow path, and further includes a differential pressure flowmeter on the downstream side of the dilution gas supply path and the filter provided in the gas flow path, and the dilution gas supply path includes A first flow path for flowing a dilution gas at a constant flow rate and a second flow path having a piezo valve for controlling the flow rate of the dilution gas are provided in parallel, and the dilution gas A differential pressure flow meter included in the supply path is provided in a third flow path provided on the downstream side from a confluence of the first flow path and the second flow path, and the piezo valve is provided with the dilution gas Gas for measuring particulate matter in exhaust gas of partial dilution type, characterized in that the opening is adjusted based on the actual flow rate of the dilution gas detected by the differential pressure flow meter included in the supply path Provide a dilution system.

  The piezo valve has a high speed response of about 0.2 to 0.5 seconds in a region where the flow rate control range is not so large. Therefore, the piezo valve has a high flow rate measurement accuracy with a piezo valve having such a high speed response. A second flow path that is combined with a differential pressure flow meter, and that allows a dilution gas at a constant flow rate to flow regardless of fluctuations in the flow rate of the exhaust gas, and a second flow that adjusts the flow rate according to the flow rate fluctuation of the exhaust gas. The flow rate of the gas used for dilution is compared because the piezo valve is controlled based on the previous flow rate detected by the differential pressure flow meter, and only the variable flow rate range is controlled. The flow rate can be measured with high accuracy and the flow rate can be controlled with high-speed responsiveness even though the flow rate is large.

  In the gas flow rate control device according to the present invention, a piezo valve having high-speed response and a differential pressure flow meter having high flow rate measurement accuracy are combined, and a constant flow of dilution gas is allowed to flow regardless of exhaust gas flow rate fluctuations. A first flow path and a second flow path that adjusts the flow according to the flow rate fluctuation of the exhaust gas are provided in parallel, and the piezo valve is controlled based on the previous flow detected by the differential pressure flow meter. In addition, since only the variable flow range is controlled, the flow rate of the gas used for dilution can be measured with high accuracy even though the flow rate of the gas used for dilution is relatively large. It can be performed with high-speed response. Therefore, according to the present invention, a gas dilution system using flow control and partial sampling corresponding to transient measurement of engine exhaust gas can be realized.

  Embodiments of the present invention will be described with reference to the drawings. 1 to 3 show an embodiment of the present invention. In FIG. 1, the same reference numerals as those in FIGS. 5 and 6 denote the same members.

  FIG. 1 schematically shows a configuration of a main part of a dilution gas flow control device according to the present invention. In this figure, reference numeral 32 denotes a dilution gas flow control device, which is an exhaust gas G flowing through an exhaust pipe 2. The part is connected to the upstream end of the dilution tunnel 4 introduced by the probe 3. The dilution gas flow control device 32 is configured as follows.

  That is, in FIG. 1, 33 and 34 are flow paths parallel to each other (hereinafter referred to as the first flow path 33 and the second flow path 34). A downstream flow path 36 (hereinafter referred to as a third flow path) is connected to the dilution tunnel 4 on the downstream side.

  The first flow path 33 uses the dilution air A set to about 70% of the maximum flow rate of the gas used for dilution (air in this embodiment) regardless of the flow rate variation of the exhaust gas G. The first flow path 33 is provided with a suction pump, for example, a roots blower pump 37 and an air filter 38, in this order, whose suction capacity can be changed by controlling the rotational speed. Reference numeral 39 denotes an inverter that controls the rotational speed of the Roots blower pump 37. The inverter 39 receives a control signal from a first comparison control circuit 66 described later.

  Further, the second flow path 34 adjusts the flow rate according to the flow rate fluctuation of the exhaust gas G, and adjusts the flow rate in the range from zero of the dilution air A to about 30% of the maximum flow rate. To do. The second flow path 34 is provided with a suction pump 40, an air filter 41, a pressure regulator 42, and a flow rate control piezo valve 43 in this order, and the downstream side of the piezo valve 43 and the downstream side of the air filter 38 join together. ing. The piezo valve 43 is configured to press and drive the valve body that opens and closes the valve opening by the distortion force of the piezo stack, and is configured as shown in FIG. 2, for example.

  That is, in FIG. 2, 44 is a main body block, and 45 and 46 are fluid inlets and fluid outlets formed in the main body block 44. 47 is a fluid flow path formed between the fluid inlet 45 and the fluid outlet 46, and an orifice block 49 having a valve port 48 on the upper surface is provided in the middle of the fluid flow path 47. A hollow valve block 50 is provided on the upper surface of the main body block 44 so as to cover the upper surface of the orifice block 49. Inside the valve block 50, a valve body 51 for adjusting the opening degree of the valve port 48 is provided. 49 is held by a diaphragm 52 provided so as to cover the upper surface of 49. The valve body 51 is normally formed with a slight gap between the upper surface of the orifice block 49 (around the upper part of the valve port 48).

  A piezo stack 53 that presses and drives the valve body 41 downward is formed by laminating a plurality of piezo elements, and is housed in a cylindrical valve case 54 that is screwed to the valve block 50. The piezo stack 53 is configured such that an upper end portion 55 thereof is fixed to a nut member 56 screwed to the upper end of the valve case 54, and a lower end output end 57 is brought into contact with the upper end of the valve body 51. Reference numeral 58 denotes a lead wire for supplying power to the piezo stack 53.

  The piezoelectric valve 43 configured as described above is distorted by applying an appropriate DC voltage by a valve driving circuit 59 (see FIG. 1) controlled by a second comparison control circuit 67 to be described later. 57 presses and drives the valve body 51 downward to adjust the distance between the valve body 51 and the valve port 48, that is, the opening degree of the valve port 48, and the flow rate adjustment response is several tens of μsec to several msec. And very fast. Such a piezo valve 43 is described in detail in, for example, Utility Model Registration No. 2516824.

  Referring back to FIG. 1, the third flow path 36 measures the total amount of dilution air A flowing through the first flow path 33 and the second flow path 34, and has a measurement accuracy. A venturi flow meter 60 as a high differential pressure flow meter is provided, and its downstream side is connected to the upstream side of the dilution tunnel 4. In the vicinity of the venturi flow meter 60, a pressure sensor 61, a differential pressure sensor 62, and a temperature sensor 63 for detecting the pressure of the air flowing through the third flow path 36 are provided.

Reference numeral 64 denotes a flow rate calculation unit that calculates the flow rate (actual flow rate) of the dilution air A flowing through the third flow path 36 based on the detection outputs of the sensors 61 to 63. 65 divides the actual flow rate q obtained in the flow rate calculation unit 64 into two signal amounts q ₁ and q ₂ (q ₁ : q ₂ = 70: 30), and the first and second comparison controls respectively. The signal distributors output to the circuits 66 and 67. In each of the comparison control circuits 66 and 67, the signal amounts q ₁ and q ₂ given by the signal distributor 65 are respectively inputted to the flow rate setting values r ₁ and r _2. And a predetermined control signal based on the comparison is sent to the inverter 39 and the valve drive circuit 67, respectively.

In the dilution gas flow control device having the above configuration, the outputs of the sensors 61 to 63 provided in the vicinity of the venturi flow meter 60 provided in the third flow path 36 are input to the flow rate calculation unit 64, and this flow rate calculation is performed. The total flow rate of the dilution air A supplied to the dilution tunnel 4 in the unit 64 is obtained. Then, the total flow rate (actual flow rate) of the dilution air A obtained by the flow rate calculation unit 64 is distributed by the signal distributor 65 so that q ₁ : q ₂ = 7: 3. 2 is supplied to two comparison control circuits 66 and 67.

In the first flow path 33, the signal amount q ₁ is compared with the set flow rate r ₁ in the comparison control circuit 66, and a predetermined control signal is sent to the inverter 39 based on this comparison. A predetermined control signal is output from the inverter 39, whereby the Roots blower pump 37 is frequency controlled, and the flow rate of the dilution air A flowing through the first flow path 33 is always the total flow rate of the dilution air A. 70% is maintained.

On the other hand, in the second flow path 34, is compared with the signal quantity q ₂ in the comparison control circuit 67 and the set flow rate r ₂ are predetermined control signal is sent to the valve drive circuit 59 based on the comparison. Then, a predetermined control signal is output from the valve drive circuit 59, whereby the opening degree of the valve port 48 in the piezo valve 43 is adjusted, and the flow rate control is performed. That is, feedback control is performed according to the amount of fluctuation of the dilution air A detected in the third flow path 36, and the flow rate of the dilution air A flowing through the second flow path 34 is controlled.

  FIG. 3 shows temporal changes in the flow rates in the three flow paths 33, 34, and 36. Reference numerals a, b, and c in the figure indicate dilution air flowing in the flow paths 33, 34, and 36, respectively. This corresponds to the flow rate of A (see FIG. 1). As shown in FIG. 3, the flow rate of the dilution air A in the first flow path 33 is always constant (no fluctuation), and the dilution air A in the second and third flow paths 34 and 36 is constant. The flow rate is changing at high speed. Since there is no change in the flow rate c of the dilution air A in the third flow path 36 in the entire range of the large flow rate region, the fluctuation range of the flow rate b of the dilution air A in the second flow path 34 is small. Therefore, the capacity of the pump 40 may be small, and the cost is reduced.

  As described above, in the dilution gas flow rate control device of the present invention, the flow rate is not measured at high speed even though the dilution air A required for the partial dilution method by partial sampling is relatively large. However, since only the variable flow rate range can be controlled with high-speed response, the entire amount of dilution air A having a relatively large flow rate can be controlled with high-speed response and high accuracy within the range of 70% from the maximum flow rate. it can.

  The present invention is not limited to the above-described embodiment, and can be implemented with various modifications. You may comprise the 1st flow path 33 as shown to FIG. 4 (A) and (B). That is, as shown in FIG. 5A, a pressure regulator 68 and a critical flow orifice 69 may be provided on the downstream side of the Roots blower pump 37 and the filter 38. Further, as shown in FIG. 5B, a flow resistance 70 such as a pressure regulator 68 and a capillary may be provided downstream of the Roots blower pump 37 and the filter 38.

  In place of the roots blower pump 40 provided in the second flow path 34, a compressor may be provided. Further, a laminar flow meter may be used in place of the venturi flow meter 60 provided in the third flow path 36.

  Furthermore, instead of dilution air, an appropriate inert gas such as nitrogen gas may be used.

It is a figure which shows schematically the structure of the principal part of the gas flow control apparatus for dilution of this invention. It is a longitudinal cross-sectional view which shows roughly the structure of the piezo valve used in the said gas flow control apparatus for dilution. It is a figure for demonstrating operation | movement of the said gas flow control apparatus for dilution. It is a figure which shows the other structure of the 1st flow path in the said gas flow control apparatus for dilution. It is a figure which shows an example of the gas dilution system of the partial dilution system by partial extraction. It is a figure which shows the structure of the conventional gas flow control apparatus for dilution.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Dilution tunnel 5 Dilution gas supply path 16, 24 Gas flow path 26, 60 Differential pressure flow meter 33 1st flow path 34 2nd flow path 35 Junction point 36 3rd flow path 43 Piezo valve A For dilution Gas G Exhaust gas S Sample gas

Claims (2)

  A dilution tunnel for diluting the partially collected exhaust gas, a dilution gas supply path connected to the upstream side of the dilution tunnel, and a gas flow path connected to the downstream side of the dilution tunnel and through which the diluted sample gas flows Each of the dilution gas supply path and the gas flow path includes a differential pressure flow meter, and the dilution gas supply path includes a first flow path for flowing a constant flow of dilution gas, and dilution. A second flow path having a piezo valve for controlling the flow rate of the working gas is provided in parallel, and a differential pressure flow meter included in the dilution gas supply path includes the first flow path and the second flow path. The piezo valve is provided in a third flow path provided downstream from the junction with the flow path, and the piezo valve is based on the actual flow rate of the dilution gas detected by the differential pressure flow meter included in the dilution gas supply path. To adjust the opening Exhaust gas measurement gas dilution system of partial dilution type which is characterized in that.   A gas dilution system for measuring particulate matter contained in exhaust gas discharged from an engine or the like, comprising a dilution tunnel for diluting a partially collected exhaust gas and a dilution connected to the upstream side of the dilution tunnel A gas supply path, a gas flow path connected to the downstream side of the dilution tunnel, through which the diluted sample gas flows, and a filter for collecting particulate matter contained in the sample gas are provided in the gas flow path. Further, a differential pressure flow meter is included on the downstream side of the filter provided in the dilution gas supply path and the gas flow path, respectively, and the dilution gas supply path is configured to flow a dilution gas at a constant flow rate. 1 flow path and a second flow path provided with a piezo valve for controlling the flow rate of the dilution gas are provided in parallel, and a differential pressure flow meter included in the dilution gas supply path includes: The piezo valve is detected by a differential pressure flow meter included in the dilution gas supply path, provided in a third flow path provided downstream from the confluence of the first flow path and the second flow path. A gas dilution system for measuring particulate matter in exhaust gas of partial dilution type, characterized in that the opening degree is adjusted based on the actual flow rate of the diluted gas.

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