Measuring and testing – Fluid pressure gauge – Combined
Reexamination Certificate
2000-12-27
2003-05-13
Williams, Hezron (Department: 2855)
Measuring and testing
Fluid pressure gauge
Combined
C073S118040, C073S118040, C073S756000
Reexamination Certificate
active
06561036
ABSTRACT:
TECHNICAL AREA
The present invention concerns a pressure sensor for the continuous measurement of gas pressure inside the cylinders of a combustion engine. The pressure sensor is consequently placed in a very severe environment with high pressure of several hundred bar and a temperature of up to 1000° C. Continuous measurement to be able to determine the pressure distribution during every working cycle in the combustion engine places heavy demands on the dynamic response of the pressure sensor to rapid processes.
The greatest area of use for continually measuring pressure sensors is in very large combustion engines which are operated at relatively low revolutions per minute. Such motors are used for example as ships engines and as stationary engines for driving electrical generators and gas compressors.
Because of the growing demands for reduced consumption of fuel and continually increasing environmental demands on the chemical composition of exhaust gases the requirement to monitor the operation of combustion engines has increased. Misfiring influences exhaust gas chemical composition and can also negatively influence the working life of a combustion engine. With the help of continuous measurement misfiring can be detected and action be taken to ensure proper functioning is regained.
The technical area in which such pressure sensors work places high demands on long term stability so that the high temperatures existing do not influence the ageing characteristics of the pressure sensor material.
THE STATE OF THE ART, THE PROBLEM
A pressure sensor for continuous measurement of gas pressure in the cylinders of combustion engines is described in U.S. Pat. No. 4,408,496. The embodiment is reproduced in
FIG. 1
which shows that the sensor comprises a tube-shaped channel
1
with circular cross section one end of which is connected to and open to the cylinder (not shown) for which the gas pressure is to be determined. The channels other and closed end consists of a relatively flexible membrane-like circular disc shaped part
2
against which the gas pressure of the cylinder connected side is to exert an affect. The circular disc shaped part is concentric relative to the tube-shaped channel and equipped with a central projection or lug
3
. The gas pressure is transferred via the channel
1
to the circular shaped disc part
2
and the central lug
3
via a force transferring means
4
to a force measuring means
5
. The force transferring means is so shaped that the force from the gas pressure which influences the circular disc shaped part is converted via the force transferring means
4
to a tension in the force measuring organ
5
. The tube-shaped channels other cylindrical surrounding parts are, because of the pressure sensors construction, regarded as very rigid. A complete system for gas pressure monitoring with a sensor according to the said U.S. Patent is described in an article “CYLDET, ASEA'S SYSTEM FOR MONITORING THE COMBUSTION PRESSURE IN DIESEL ENGINES” presented at the American Society of Mechanical Engineers Meet Apr. 5-10, 1975 (75-DGP-11).
In the periodical MARINE ENGINEERS REVIEW, October 1995 there is an advertisement with “Reader ref. A1037” which summarily presents a pressure sensor SEC ENGINE ANALYZER. In the reference it is clear that the gas pressure, via a circular cross-sectioned, relatively thin walled tube of which one end is open to a cylinder which is not shown, is able to influence the circular end surface of the channels closed other end. The tube is connected, via welds in the tube ends, to a membrane of magnetic material. The membrane is mechanically pre-tensioned and in contact with the tube via the welds. Between the membrane and the cylindrical tube there is a column for thermal insulation. Gas pressure is determined indirectly using changes in the length of the tube as the starting point. The connected membrane is made to vibrate with the help of magnetic coils and the reference claims that the square of the changes in frequency of the vibrations are proportional to the actual gas pressure.
The disadvantage with that construction is that the membrane and tube have dissimilar temperature coefficients which leads to large variations arising in the tension in the membrane which solely depend on the temperature and which become interpreted as a pressure change. Even more serious is the fact that the tube is subjected with every pressure pulse to a corresponding adiabatic thermal pulse from compressed gas. This pulse causes in turn a dynamic change in length of the tube which is also received as a pressure change by the measuring system. Taken together this means that the pressure sensor introduces a dynamic measuring error which varies with peak pressure and frequency.
In a brochure from KISTLER, “KISTLER INFORMATION 53, DECEMBER 1996” a pressure sensor is described as consisting of a thick walled tube with a cross section in the form of a circular ring. Axially a part of the tube with a cross section corresponding to a sector of a circle has been removed. The effect of cylinder pressure in the tubes inner cavity causes the tube to expand in a tangential direction proportional to the cylinder pressure. The expansion is determined with a piezoelectric element. The disadvantage with a pressure sensor based on piezo crystals is that they measure only dynamic pressure and consequently cannot be used to measure static pressure. Even here there is a dynamic displacement pulse which depends the corresponding thermal-adiabatic thermal pulse in the gas. Measuring errors such as these have great significance in the evaluation of the efficiency of a cylinder in a motor.
Thus a circular cylindrical tube with an opening to a cylinder and a closed other end is subjected to cylinder pressure and that cylinder pressure will influence both the axial length and the diameter of the tube. In the above mentioned US-patent the force with which the cylinder pressure influences the closed end is used and in the above mentioned SEC ENGINE ANALYZER the changes in axial length caused by cylinder pressure are used for the determination of cylinder pressure. The changes in diameter in the circular cylinder tube can still not be used for the determination of cylinder pressure on the grounds that there is a column between the measuring membrane and the pressure cylinder and that a extension cannot be transferred via the column.
In GB 1389408 a device for the measurement of the pressure of a fluid in a circular tube is shown, with an embodiment adapted to measure the gas pressure from a cylinder. The measuring section of the tube is circular in cross section.
From GB 2019007 a similar device is shown for measuring gas pressure in a cylinder. It is known from this device to use a tube in which the walls on the outside surface of the tube in the measuring section form two plane parallel surfaces. From U.S. Pat. No. 4,290,311 it known to measure the pressure in a tube where two transducers are held against the tube. The tube is circular in cross section at the point of measurement. The transducers in the form of strain gauges are held between two parallel parts and the contact faces of the transducers have been shaped to conform to the circular tube. From U.S. Pat. No. 3,898,885 it is known to use a tube with circular cross section to measure the fluid pressure in a flexible hose. From GB 2198239 it is known to use a tube with plane parallel measuring surfaces to measure the fluid pressure in a flexible hose. From U.S. Pat. No. 5,044,203 it is also known to use a tube with plane parallel measuring surfaces to measure the fluid pressure in a flexible hose.
DESCRIPTION OF THE INVENTION, ADVANTAGES
A pressure sensor according to the invention also comprises a tube one end of which is open to a cylinder for which the gas pressure will be measured. The other end of the tube is closed in the same way according to the state of the art. The invention consists in that the tube is shaped in such a way that movements in the walls of the tube can be used for the determination of cylinder
Gustafsson Pär
Kolavcic Pavel
Lifvenborg Ulf
ABB AB
Dykema Gossett PLLC
Mack Corey D.
Williams Hezron
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