Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
1998-02-27
2001-05-08
Fuller, Benjamin R. (Department: 3747)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06227058
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a high precision flow meter for measuring a gaseous volume flow in a pipe. In particular, the invention relates to a high time resolution flow meter for measuring the volume flow of an exhaust gas in a pipe of an internal combustion engine.
In the prior art, flow meters are used for monitoring the time history of an exhaust gas flow of an internal combustion engine during various testing cycles of the engine, in which different driving conditions of a motor vehicle are simulated.
From the dissertation of Mr. Andreas Hess, Langstra&bgr;e 18, 7526 Weiher, Germany, titled “Sensor for Dynamic Volume Flow Determination in a Diluted Exhaust Gas of a Motor Vehicle”, which was written in co-operation with the Politechnic Mannheim, Department Communication Engineering, dated 1993, it is known to determine the volume flow of an exhaust gas by measuring the run time differences of ultrasonic signals travelling obliqely through the volume flow from a first sonic transmitter to a first sonic receiver and substantially in the opposite direction from a second sonic transmitter to a second sonic receiver on the basis of the so-called “run time difference method”. According to this method, the average velocity of the volume flow of the exhaust gas in a pipe is determined on basis of the angle between the travelling path of the sonic signals and the volume flow and the length of the travelling path by measuring the run time differences of the sonic signals which are caused by an addition or a substraction of the velocity of the volume flow and the associated components of the speed of the sonic signals, respectively. By multiplying the determined velocity of the volume flow and the cross section of the pipe, the instantaneous average volume flow of the exhaust gas can be determined. In the apparatus described in the dissertation, piezo crystals which are disposed opposite to each other, are used for generating and receiving the sonic signals. Each of the piezo crystals is operated as a transmitter and a receiver at substantially the same time. Due to transient effects or phenomena which are caused as a result of the inertia of the piezo crystals, and which leads to a comparatively large error in the determination of the exact measuring time at which a sonic signal is transmitted or received, the described apparatus has a comparatively low accuracy in determining the volume flow. Moreover, due to the unfavourable vibrational properties of the piezo crystals, the apparatus does not allow for measuring a volume flow with a sufficient time resolution, as it is required for determining and verifying the amount of pollutants generated during a testing cycle. Moreover, it is a disadvantage of the described apparatus that the piezo crystals are in direct contact with the corrosive and hot exhaust gas. As a result of the direct contact between the crystals and the exaust gas, the operational life time of the crystals is strongly reduced and a further measurement error is caused by the thermal behaviour of the piezo crystals.
In addition, the “run time difference method” is also described in the article titled “Dubbel”, Edition 18, page W 16, Springerverlag.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a flow meter which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type, and which is capable of determining the volume flow of a gas, in particular, an exhaust gas of an internal combustion engine with improved accuracy and time resolution. It is a further object of the invention, to provide for a method and an apparatus which allows for an enhanced measuring accuracy without employing additional sensors, when determining the velocity of a volume flow of a gas in a pipe on basis of the run time difference method.
With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for measuring a volume flow of a gaseous medium in a pipe, including a first sonic transmitter which generates first sonic signals; a predetermined path which has a first end and a second end disposed obliquely to the volume flow, the first sonic signals passing the volume flow along the predetermined path from the first end to the second end; a second sonic transmitter which generates second sonic signals, the second sonic signals following the path from the second end to the first end of the path; a first and a second sonic receiver for receiving the first and the second sonic signals after the first and the second sonic signals have traveled the path and for converting the first and the second sonic signals into respective first and second electronic signals; and a control and measuring unit, the control and measuring unit determines a respective run time of the first and the second sonic signals and further determines a speed of the volume flow on the basis of the run times, wherein the first sonic transmitter and the second sonic receiver are disposed relative to each other for causing at least a part of the first sonic signals before traveling the path, to impinge upon the second sonic receiver for generating a first trigger signal used by the control and measuring unit to determine the run times of the first sonic signals.
In accordance with an added feature of the invention, the second sonic transmitter and the first sonic receiver are disposed relative to each other to impinge at least a part of the second sonic signals on the first sonic receiver before traveling along the path for generating a second trigger signal used by the control and measuring unit to determine the run time of the second sonic signals.
In accordance with another feature of the invention, there is a first deflecting mirror which has a reflecting surface and a focus disposed at a given distance from the first sonic transmitter, the first deflecting mirror directs the first sonic signals in a direction towards the first sonic receiver, and the second sonic receiver is disposed in the reflecting surface of the first deflecting mirror.
In accordance with an additional feature of the invention, the first deflecting mirror is a parabolic mirror and the first sonic transmitter is disposed in the focus of the first deflecting mirror.
In accordance with yet another added feature of the invention, there is a second deflecting mirror which has a reflecting surface and a focus disposed at a given distance from the second sonic transmitter, the second deflecting mirror directs the second sonic signals in a direction towards the second sonic receiver, and the first sonic receiver is disposed in the reflecting surface of the second deflecting mirror.
In accordance with yet another feature of the invention, the second deflecting mirror is a parabolic mirror and the second sonic transmitter is disposed in the focus of the second deflecting mirror.
In accordance with yet another additional feature of the invention, there are grids located at least at one of the first end and the second end of the path, the grids are permeable to the first and the second sonic signals and substantially non-permeable to the volume flow.
In accordance with yet a further added feature of the invention, at least one of the first and the second sonic transmitters have an electric spark gap, and the first and the second sonic signals are generated by a spark discharge.
In accordance with yet a further additional feature of the invention, the spark gap has a first and a second electrode, the first and the second electrode each have a tip, and includes a discharge plane disposed between and above the electrodes to generate a defined spark discharge exclusively across the discharge plane.
In accordance with an added feature of the invention, the discharge plane is made of a material including Quartz.
In accordance with another feature of the invention, there is a projection formed of an insulating material, and wherein at least one of the first and the second electrode of the spark gap is sp
Fuller Benjamin R.
Greenberg Laurence A.
Lerner Herbert L.
Peus-Systems GmbH
Stemer Werner H.
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