Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
2002-07-19
2003-11-04
Williams, Hezron (Department: 2856)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S727000
Reexamination Certificate
active
06640644
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to sensor assemblies and in particular to a sensor assembly including a piezoresistive membrane for detecting he tilt and vibration of a body and for generating output signals indicative of the tilt and vibration detection.
Today's automobiles and similar vehicles typically include highly sophisticated and complex systems and rely on control systems that receive input signals from a variety of sensing devices. Automobiles and similar vehicles powered by internal combustion engines depend on lubricating fluids such as oil for lubricating moving components of the engine and to help maintain the engine at a proper operating temperature. Oil refining and formulation itself has become a complex process to ensure that internal combustion engines are properly lubricated and cooled during operation while taking into account environmental conditions. It is well known that oil quality varies and that over time the level of oil within an engine may be reduced due to leaks and/or oil combustion and the condition of oil deteriorates. Consequently, numerous types of electronic sensors and sensor assemblies have been developed to monitor and/or detect oil level, oil temperature, and oil condition, for example. These sensors and assemblies may include algorithms that depend on determining whether a vehicle is parked on an incline and/or whether a vehicle's engine is running or shutdown. Oil level measuring algorithms are known in the art. Some are known to use averaging techniques to dampen the affect of an automobile being parked on an incline when the oil level measurement is taken. Other algorithms or methods may only take an oil level measurement when it is known that a vehicle is parked on a level surface.
Many tilt sensors are of the electrolytic type. A typical electrolytic sensor includes a glass or ceramic envelope that is partially filled with a conductive fluid. The fluid moves in response to tilting of the sensor where the fluid is under the influence of gravity, such as with a carpenter's spirit level. In other embodiments the fluid may be under the influence of the acceleration of a body. Platinum contacts may be sealed flush with the inside walls of the envelope. When such a sensor is at its zero position the electrical impedance of the fluid from the center electrode to each of the left and right electrodes is equal. Tilting the sensor disturbs this balanced condition and the impedance changes in proportion to the tilt angle. Cost and size of a typical electrolytic sensor limit their use in certain environments. Many electrolytic sensors are sensitive to temperature change and temperature compensation needs to be provided in most of the signal conditioning electronic units. Also, with respect to glass electrolytic sensors, great care must be afforded to the thermal and mechanical stress related characteristics of glass during installation and alignment. This may limit the range of applications of such sensors.
Another known category of tilt sensor types is switch sensors, which may be a variation of an electrolytic sensor. A switch type tilt sensor doesn't use a linear output with respect to inclination angle. Instead, a signal is generated once the inclination reaches a predetermined threshold.
While not used specifically for detecting the tilt of a body, a common structure for measuring pressure are pressure transducers. Pressure transducers may be diaphragm-based transducers that convert an applied pressure into stresses in the plane of the diaphragm. The stresses may be measured and converted into electrical signals by use of piezoresistive sensors that are an integral part of the diaphragm. Depending on the application, the diaphragm may be fabricated of metal or a semiconductor material such as silicon. Such configurations are known to be used in microphones, the automotive industry such as for checking tire, gas and air pressure, the biomedical industry such as for determining blood and fluid pressure, various instrumentation and vacuum sensing.
A known configuration for such an arrangement may be semiconductor devices with the resistive bridge legs formed such as by appropriate doping of selected portions of material in the semiconductor material. For example, U.S. Pat. No. 5,614,678 discloses a device using semiconductor material that is lightly doped N- or P-type silicon in a portion of the crystallographic plane. The piezoresistive elements of that device may be fabricated from P+ or P++ silicon in the crystallographic plane using known techniques. The piezoresistive sensing elements may be arranged in a Wheatstone bridge circuit so that two piezoresistors are positive changing and the other two are negative changing. The disclosed arrangement allows for an output voltage to be generated, which is indicative of an applied pressure on the device.
The condition of the lubricant such as the oil of an internal combustion engine is an important factor in determining whether fresh lubricant needs to be added to a system or whether the lubricant needs to be changed. Some such algorithms or methods may depend on an ignition signal to determine whether the engine is running or shutdown. Ignition signals are not always indicative of whether the engine is actually running or shutdown and may thereby adversely affect the oil condition algorithm or method.
Considering the cost and size advantages of using a semiconductor sensor relative to known tilt sensor types such as an electrolytic sensor, for example, it would be advantageous to provide a low cost semiconductor sensor for detecting tilt that could be adapted for a range of environments such as those requiring small scales in size. It would also be advantageous to provide a senor for accurately determining whether an automobile's engine was running or shutdown.
BRIEF SUMMARY OF THE INVENTION
An exemplary embodiment of an apparatus in accordance with one aspect of the present invention allows for the detection of certain operational parameters associated with a structure or a vehicle such as an automobile. For example, one exemplary embodiment may include an apparatus for detecting the tilt of the automobile relative to a reference position such as horizontal and vibration of the automobile. Vibration of the automobile may be used to determine whether the automobile's engine is running, e.g., the automobile has been started and the engine is idling or generating higher revolutions per minute (“RPM”) than that of idling.
One exemplary embodiment of the present invention allows for electronic data indicative of engine running and vehicle tilt to be output from the apparatus and transmitted to a microcontroller or processor of the automobile for data analysis. The microcontroller or processor may send electronic signals indicative of output from the analyzed data to a display device such as a driver information center of an automobile, for example.
One exemplary embodiment for detecting tilt and vibration of a body in accordance with one aspect of the present invention takes advantage of the crystallographic structure and piezoresistive effect in semiconductor materials. The body may be a commercial or private vehicle, for example, or it could be any other physical structure where detecting tilt and/or vibration is desired. Such an apparatus may include a membrane where a plurality of piezoresistors may be diffused onto the membrane. A weight may be integral to the membrane and placed near the membrane's center. In one exemplary embodiment four piezoresistors are diffused onto or formed integral with the membrane to form a conventional Wheatstone bridge circuit. A constant voltage input may be applied to the membrane. A change in resistance of one or more of the piezoresistors may be used to create a first voltage output signal and a second voltage output signal by means of the Wheatstone bridge. The first voltage output signal may be responsive to the angular displacement or tilt of the membrane from a refere
Almaraz Jose L
Mireles Pedro G
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Williams Hezron
Wilson Katina
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