Measuring and testing – Liquid level or depth gauge – Hydrostatic pressure type
Reexamination Certificate
1999-09-03
2001-10-09
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Hydrostatic pressure type
C073S29000R, C073S302000, C367S149000
Reexamination Certificate
active
06298721
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to measurement systems and, more particularly, to a continuous liquid level measurement system.
BACKGROUND OF THE INVENTION
In the field of internal combustion engines, it is often desirable to measure the level of various engine liquid levels, such as engine oil, fuel, coolant, etc. In the case of engine oil, for example, engines are nearly always provided with an oil dipstick which is extended down a tube and into the engine oil pan. By withdrawing the dipstick, the amount of oil in the oil pan may be roughly determined by visually inspecting the distance from the distal end of the dipstick to the uppermost reach of the oil clinging thereto.
This method for measuring oil exhibits several drawbacks. First, the visual measurement is an extremely vague measurement in terms of quantity of oil. In some instances, for example, it is desired to measure the amount of oil consumed by an engine versus time, in a long-term test in which the engine is operated continuously over an extended period. In such instances, a dipstick does not provide satisfactory measurement resolution or repeatability. Also, dipsticks are inconvenient from a measurement time standpoint, such as for use in fleet vehicles where it is desired to measure the oil level on a daily basis.
Attempts have therefore been made in the prior art to provide for automated electronic sensing of fluid levels such as engine oil levels. Such measurements can be problematic due to the harsh environment in which the measurement must be made. For example, the use of capacitive sensors in the oil pan are generally unreliable due to the high soot environment of the engine oil. Furthermore, oil pans experience high vibration levels when the engine is operating, making it difficult to maintain pressure transducer based measurement systems in the oil pan. Also, oil pan durability can be compromised when mounting sensors therein.
Another problem encountered when trying to measure oil level in the oil pan by measuring the pressure exerted by the oil on a pressure sensor is the inaccuracy of such measurements caused by varying head pressure above the oil (caused by blowby gases and the dynamics of the moving engine parts). Varying head pressure can also be a problem in other closed vessels, such as fuel tanks and coolant tanks.
There is therefore a need for an accurate liquid level measurement system that may be read automatically, that avoids reliability problems associated with a harsh measurement environment, and that produces an accurate level measurement, even with varying head pressures. The present invention is directed toward meeting this need.
SUMMARY OF THE INVENTION
A continuous liquid level measurement system is disclosed which is based upon a differential pressure measurement. The pressure of the liquid level to be measured is calibrated with a second pressure measurement of the pressure above the liquid in order to get a more accurate pressure measurement which is related in a predetermined manner to the level of the liquid. For instances in which the liquid to be measured is in a harsh environment, the invention provides for a means for mounting the sensitive pressure measurement devices remotely from the liquid.
In one form of the present invention, a continuous liquid level measurement system is disclosed, comprising a shaft having a proximal end and a distal end; a differential pressure transducer disposed at the proximal end and having a first pressure input and a second pressure input; a flexible bladder disposed at the distal end; a first pressure transmission tube disposed within the shaft and coupling the bladder to the first pressure input for substantial equalization of pressure therebetween; a reference pressure port formed in the shaft proximal of the bladder; and a second pressure transmission tube disposed within the shaft and coupling the reference pressure port to the second pressure input for substantial equalization of pressure therebetween; wherein when the bladder is placed below the liquid level and the reference pressure port is placed above the liquid level, the differential pressure transducer will measure a pressure of the liquid on the bladder, and thus the liquid level.
In another form of the present invention, a continuous liquid level measurement system is disclosed, comprising a shaft having a proximal end and a distal end; a first pressure transducer disposed at the proximal end and having a first pressure input and a first pressure output signal; a second pressure transducer disposed at the proximal end and having a second pressure input and a second pressure output signal; a signal processor coupled to the first and second pressure output signals and operative to produce a difference output signal substantially equal to a difference between the first and second pressure output signals; a flexible bladder disposed at the distal end; a first pressure transmission tube disposed within the shaft and coupling the bladder to the first pressure input for substantial equalization of pressure therebetween; a reference pressure port formed in the shaft proximal of the bladder; and a second pressure transmission tube disposed within the shaft and coupling the reference pressure port to the second pressure input for substantial equalization of pressure therebetween; wherein when the bladder is placed below the liquid level and the reference pressure port is placed above the liquid level, the difference output signal will be proportional to a pressure of the liquid on the bladder, and thus the liquid level.
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Dringenburg Dean H.
French Mike
Schneider Matthew L.
Schuppe Alfred
Weng Weibo
Cummins Engine Company, Inc.
Loo Dennis
Williams Hezron
Woodard Emhardt Naughton Moriarty & McNett
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