Stable, reliable capacitive oil deterioration and level sensor

Details Stable, reliable capacitive oil deterioration and level sensor Stable, reliable capacitive oil deterioration and level sensor

2000-11-10

2001-10-02

Hofsass, Jeffery (Department: 2632)

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

C340S450000, C340S450100, C340S450200, C340S451000, C340S452000

Reexamination Certificate

active

06297733

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-functional sensor and, more particularly, pertains to a design of a reliable capacitive oil deterioration and level sensor whose measurements are insensitive to changes in the operating environment of the sensor.
2. Description of the Related Art
One of the most important factors that contributes to the efficiency and durability of internal combustion engines is lubrication. As engine oil “breaks down” it is less effective in protecting an engine from damage caused by friction between engine parts. More specifically, the normal life span of motor oils is limited by thermal breakdown, additive depletion and carbon particulates that result from the combustion process.
The deterioration of engine oil is marked by a decrease in the viscosity of the oil. The dielectric constant of engine oil provides an indication of the oil's deterioration or lack thereof.
The dielectric constant of motor oil is typically between 1.6 and 3.2 depending upon its brand and age. For example, the dielectric constant of a particular brand of motor oil may increase from 2.19 to 3.2 after 400 hours of use in a particular internal combustion engine under certain operating conditions. Thus, it is desirable to have a means for indicating reliably when engine oil has deteriorated to the point where it should be changed.
Premature lubrication failure can also result from the presence of contaminants in the engine oil such as coolant (glycol ethylene), filel or water. The presence of these contaminants in motor oil is often indicative of a mechanical failure such as a damaged head gasket or a broken piston ring. Water and engine coolant have dielectric constants of approximately 87.5 and 37.0, respectively. The introduction of such contaminants into the engine oil significantly increases the dielectric constant of some of the fluid which circulates through the engine for the purpose of lubrication. Thus, it is also desirable to have a means for detecting the presence of these substances in engine oil.
The dielectric constant of oil is also influenced by the temperature of the oil and by the specific formulation of a given brand of oil. Thus, it is also desirable to provide a multi-functional sensor with a means for compensating for changes in the dielectric constant of oil resulting from these factors.
U.S. Pat. No. 5,929,754 of Dr. K. M. Park et al. discloses a high-sensitivity capacitive oil deterioration and level sensor that measures the dielectric constant of the liquid suspension. However, under certain circumstances, the output of this sensor has not been as stable as would be desired.
Accordingly, a principal object of the present invention is to increase the stability and reliability of sensors of the type disclosed in the above-identified patent.
SUMMARY OF THE INVENTION
It has been determined that the undesired variations in the output of the sensors of the type shown in the patent cited above may arise from (1) the presence of nearby moving objects such as a crankshaft or other metallic objects, and (2) current flow between the capacitive electrodes which may result in a build-up of a material on at least one of the electrodes.
Accordingly, a more specific object of the present invention is to include a protection mechanism for the high-sensitivity capacitive oil deterioration and level sensor, such that the presence of nearby moving parts do not affect the output from the sensor, thereby providing more reliable measurements.
Another specific object is to provide an isolation for the electrodes of the high-sensitivity capacitive oil deterioration and level sensor so as to eliminate unwanted flow of current between the electrodes, which can adversely affect the measurements from the sensor.
In accordance with a specific illustrative embodiment of the present invention, a reliable capacitive oil deterioration and level sensor includes an inner member (electrode), and a combined outer electrode and shielding member (hereupon referred to as a shield-electrode). The outer shield-electrode may also be a part of the housing of the sensor system, and this entire subassembly may be at ground potential. The sensor also preferably includes an electrical connector and associated electronics. The housing member may include a threaded outer surface adapted to be threaded into the oil pan of an internal combustion engine.
The outer shield-electrode has at least one port sized to allow oil within the oil pan to flow into and through a space between the outer shield-electrode and the inner electrode. The shield-electrode protects the sensor assembly from the effect of moving objects such as a crankshaft and/or metallic objects. The inner electrode includes a cylindrical portion with an outer surface defining a measuring electrode. The inner electrode is secured within the housing member by an insulating spacer such that the outer grounded shield-electrode, and the inner measuring electrode define an oil deterioration and level sensor variable capacitor. An electrical connector is adapted to provide an electrical interface to a processor.
The provided electronics within the housing member may include a reference capacitor. The reference capacitor can also be located external to the electronics. The electronics are electrically connected to the oil deterioration and level sensor capacitor, the reference capacitor, and the electrical connector. The electronics are adapted to generate an oil deterioration output signal and an oil level output signal employing the oil deterioration and level sensor capacitor and the reference capacitor and to provide signals to the electrical connector.
The electronics within the housing member contain additional isolating capacitors. The isolating capacitors have a magnitude at least several times greater than the capacitance of the variable and the reference capacitor. Preferably two isolating capacitors are used, one in series with each of the variable and reference capacitors on either side thereof. However, in some cases a single isolating capacitor between a common output point of the variable, fixed capacitors and ground may be effective. The isolating capacitors prevent any net flow of direct current between the two electrodes, and therefore avoid any build-up of material at either electrode, which might otherwise adversely change the sensor output.


REFERENCES:
patent: 5060108 (1991-10-01), Baker et al.
patent: 5233875 (1993-08-01), Obermeier et al.
patent: 5329819 (1994-07-01), Park et al.
patent: 5929754 (1999-07-01), Park et al.

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