JP2000035821A - Gas flow rate controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control gas such as air with a high speed response and high precision by adjusting the opening of a piezo valve based on a result obtained by comparing a real flow rate obtained by a differential pressure flow meter with a setting flow rate. SOLUTION: A piezo valve 33 provided with high speed responsiveness and a venturi flow meter 10 having high flow rate measurement precision are connected in series. A real flow rate obtained by the venturi flow meter 10 is compared with a setting flow rate and the opening of the piezo valve 33 is adjusted based on the result. Thus, gas such as air is controlled with a high speed response and high precision. A circuit 49 driving the piezo valve 33 receives a signal from a comparison control circuit 15 and adjusts the opening of the valve opening of the piezo valve 33. The piezo valve 33 applies suitable DC voltage to a piezo stack and therefore respective piezo elements are distorted. An output terminal presses a valve body downward, drives it and adjusts the opening of the valve opening. The responsiveness of flow rate adjustment is the considerably high speed of several 10 μ sec-several msec, for example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling a flow rate of a gas such as air.

[0002]

2. Description of the Related Art Fine particulate matter (P) such as soot contained in gas discharged from a diesel engine of an automobile or the like is used.
In recent years, as a gas dilution system necessary for measurement of articulate matter (PM), flow rate control and partial sampling of exhaust gas have replaced the conventional full dilution system that collects and dilutes the entire amount of exhaust gas. A small-scale dilution system of a partial dilution system for performing the above-mentioned method has been adopted. This partial dilution type dilution system controls the flow rate of the exhaust gas dilution air while maintaining the exhaust gas after dilution at a constant flow rate, thereby controlling the exhaust gas sampling flow rate obtained as the difference between these flow rates. System.

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

[0004] That is, in FIG. 4, a roots blower pump 7 provided in the flow path 8 and capable of changing the suction capacity by, for example, controlling the number of rotations is controlled by an inverter (frequency converter) 9. Reference numeral 10 denotes a Venturi flow meter as a differential pressure flow meter having high measurement accuracy, and a pressure sensor 11 for detecting a pressure of air flowing through the flow path 8 near the Venturi flow meter.
A differential pressure sensor 12 and a temperature sensor 13 are provided. Reference numeral 14 denotes a flow rate calculation unit that calculates the flow rate (actual flow rate) of the air flowing through the flow path 8 based on the detection outputs of the sensors 10 to 13. 15 compares the actual flow rate of air obtained in the flow rate calculation unit with a preset flow rate,
This is a comparison control circuit that outputs a predetermined control signal to the inverter 9.

Reference numeral 16 denotes a gas passage connected to the downstream side of the dilution tunnel 4 and through which the diluted sample gas S flows. The downstream side of the passage 16 is branched into two passages 17 and 18.
Filters 19 and 20 for trapping PM contained in the sample gas and control valves 21 and 22 capable of varying the throttle amount (pressure loss) are provided in the respective flow paths 17 and 18, and one flow path 17 is fixed. The sample gas flow path for flowing the exhaust gas at all times, and the other flow path 18 are each configured as a bypass flow path for flowing the exhaust gas in an unsteady state.

Reference numeral 23 denotes a three-way solenoid valve provided as a flow path switching means provided downstream of the sample gas flow path 17 and the bypass flow path 18. The port 23a is in the sample gas flow path 17, and the port 23b is in the bypass flow path. 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 has a suction pump whose suction capacity can be changed by controlling the number of rotations.
For example, a roots blower pump 25 and a differential pressure flow meter with high measurement accuracy, for example, a Venturi flow meter 26 are provided in this order. 27 is a pressure sensor for detecting the pressure of the gas flowing through the gas passage 24, 28 is a differential pressure sensor, 29
Is a temperature sensor.

Reference numeral 30 denotes an inverter (frequency converter) for controlling the roots blower pump 25, and reference numeral 31 denotes a flow control unit for controlling the entire apparatus. The flow control unit 31 outputs a command to the control valves 21 and 22 and the inverter 30, and outputs a command to the sensors 27 to 29.
Is input.

Thus, in the above gas dilution system,
A command value is output from the comparison control circuit 15 to the inverter 9, and the roots blower pump 7 provided in the flow path 8 is controlled based on the command value, so that a predetermined flow rate of dilution air is supplied to the dilution tunnel 4. On the other hand, a command value output by a PID controller (not shown) provided in the flow control unit 31 is output to the inverter 30, and based on the command value, the roots blower pump is output based on the command value output from the inverter 30. By controlling the flow rate 25, the flow rate S of the sample gas flowing through the gas flow paths 16, 18, 24 is controlled so as to be always a predetermined flow rate, thereby controlling the flow rate at which the exhaust gas is collected.

[0010]

However, in the dilution gas flow control device 6 having the above-described structure, the pump 7 and the venturi flow meter 10 are provided in series with each other, so that there are the following inconveniences.

That is, the Venturi flow meter 10 as a means for measuring the air flow rate has a high flow rate measurement accuracy of about ± 0.1 to 0.2% in a flow rate range near its full scale. The pump 7 as a means for controlling the air flow rate changes the flow rate by its rotation. Due to the inherent inertia of the pump, the flow rate control response speed is:
The limit was about 0.5 to 1 second.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to provide a gas flow control device capable of controlling gas such as air at high speed and with high accuracy.

[0013]

To achieve the above object, a gas flow control device according to the present invention is provided with a piezo valve and a differential pressure flow meter in a flow path of a gas so as to be in series with each other. The actual flow rate obtained by the pressure flow meter is compared with a set flow rate, and the opening of the piezo valve is adjusted based on the comparison result.

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 having such a high-speed response and a high flow rate measurement In a gas flow control device that combines an accurate differential pressure flow meter, compares the actual flow rate obtained by the differential pressure flow meter with a set flow rate, and adjusts the opening of the piezo valve based on the comparison result. In addition, gas such as air can be controlled at high speed and with high accuracy.

[0015]

Embodiments of the present invention will be described with reference to the drawings. FIGS. 1 and 2 show one embodiment of the present invention. In FIG. 1, the same members as those in FIG. 4 indicate the same members.

FIG. 1 shows a gas flow control device 32 according to the present invention.
Schematically shows the overall configuration of
Reference numeral 3 denotes a piezo valve provided in the flow path 8, which is provided in series with the Venturi flow meter 10 and upstream of the Venturi flow meter 10. The piezo valve 33 drives the valve element that opens and closes the valve opening by pressing the piezo stack by the strain force, and is configured as shown in FIG. 2, for example.

That is, in FIG. 2, 34 is a main body block, and 35 and 36 are a fluid inlet and a fluid outlet formed in the main body block 34. Reference numeral 37 denotes a fluid passage formed between the fluid inlet 35 and the fluid outlet 36.
Is provided with an orifice block 39 having a valve port 38 on the upper surface. Reference numeral 40 denotes a hollow valve block provided on the upper surface of the main body block 34 so as to cover the upper surface of the orifice block 39. In the valve block 40, a valve element 41 for adjusting the opening of the valve port 38 is provided. 39 is held so as to be able to move up and down by a diaphragm 42 provided so as to cover the upper surface. Normally, a slight gap is formed between the valve body 41 and the upper surface of the orifice block 39 (around the upper portion of the valve port 38).

Reference numeral 43 denotes a piezo stack for pressing and driving the valve body 41 downward. The piezo stack 43 is formed by laminating a plurality of piezo elements, and is a cylindrical valve case 4 screwed to the valve block 40.
4. The piezo stack 43 has an upper end 45 fixed to a nut member 46 screwed to the upper end of the valve case 44, and a lower end output end 47 connected to the valve body 40.
It is configured to contact the upper end of the. Reference numeral 48 denotes a lead wire for supplying power to the piezo stack 43.

In the piezo valve 32 having the above-described structure, when an appropriate DC voltage is applied to the piezo stack 43, each piezo element is distorted, and the distortion causes the output end 47 to drive the valve element 41 downward to drive the valve element 41. The distance between the valve port 38 and the opening of the valve port 38 is adjusted, and the response of the flow rate adjustment is as fast as several tens μsec to several msec. It should be noted that such a piezo valve 33 is described in detail in, for example, Japanese Utility Model Registration No. 2516824.

Referring again to FIG. 1, reference numeral 49 denotes a circuit for driving the piezo valve 33, which receives a signal from the comparison control circuit 15 and adjusts the opening of the valve port 38 of the piezo valve 33 based on this signal. The suction pump 50 and the filter 5 are located upstream of the piezo valve 33 in the flow path 8.
1. A pressure regulator 52 is provided.

In the gas flow control device 32 having the above-described structure, the piezo valve 33 having high-speed response and the Venturi flow meter 10 having high flow rate measurement accuracy are connected in series with each other. By comparing the flow rate with the set flow rate and adjusting the opening of the piezo valve 33 based on the comparison result, gas such as air can be controlled at high speed and with high accuracy. Therefore, when the gas flow control device 32 having such excellent characteristics is incorporated in the dilution gas flow control device shown in FIG. 3 (connected to the upstream side of the air supply path 5), transient measurement of engine exhaust gas is performed. A high-speed response and high-precision dilution air control system required for the above is obtained, whereby the desired PM measurement can be performed reliably and with high accuracy.

The present invention is not limited to the above-described embodiment. For example, instead of the venturi flow meter 10, a laminar flow meter which mainly detects a flow rate by a differential pressure sensor is used. Is also good. Further, a compressor may be used instead of the pump 50.

In the above-described embodiment, the gas flow control device is used as a quantitative supply device of the dilution air in the gas dilution system for measuring the engine exhaust gas. The present invention is not limited to this, and can be widely used for controlling various gases including air at high speed and with high accuracy.

[0024]

According to the gas flow control device of the present invention, the actual flow rate obtained by the differential pressure flow meter is obtained by combining a piezo valve having excellent responsiveness of flow control and a differential pressure flow meter having high flow rate measurement accuracy. Is compared with the set flow rate, and the opening degree of the piezo valve is adjusted based on the comparison result, so that various gases such as air can be controlled at high speed and with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an overall configuration of a gas flow control device of the present invention.

FIG. 2 is a longitudinal sectional view schematically showing a configuration of a piezo valve used in the gas flow control device.

FIG. 3 is a diagram showing an example of a partial dilution type gas sample system.

FIG. 4 is a diagram schematically showing an overall configuration of a conventional gas flow control device.

[Explanation of symbols]

 8: flow path, 10: differential pressure flow meter, 33: piezo valve.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3H062 AA02 AA15 BB01 BB10 CC07 CC15 DD01 EE06 FF07 HH02 HH10 5H004 GA02 GB12 HA02 HB01 HB02 HB03 JB11 LA17 LA20 5H307 AA11 AA15 BB02 DD01 DD03 EE02 FF12 FF12 FF12 JJ03

Claims (1)

[Claims] 1. A piezo valve and a differential pressure flow meter are provided in a flow path in which gas flows so as to be in series with each other, and an actual flow rate obtained by the differential pressure flow meter is compared with a set flow rate. A gas flow control device, wherein the opening of a piezo valve is adjusted based on the pressure.