Measuring and testing – With fluid pressure – Motor part or auxiliary
Reexamination Certificate
1999-04-12
2001-05-08
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Motor part or auxiliary
C250S303000, C210S739000
Reexamination Certificate
active
06227038
ABSTRACT:
TECHNICAL FIELD
This invention pertains to a method for detecting the leakage of engine coolant into the engine oil. The method is, for example, particularly useful in detecting coolant leaks and leak paths in the head gasket area of an internal combustion piston engine. More specifically, this invention pertains to the use of a radiotracer in such a method.
BACKGROUND OF THE INVENTION
It is well known that separate, but sometimes closely spaced, quantities of coolant and lubrication oil are employed in the operation of liquid-cooled, internal combustion piston engines. In the construction of such engines, an engine cylinder block is employed in a closely fitting, sealing relationship with a cylinder head block. Depending upon its configuration of cylinders (e.g., “in line” or “V”), the cylinder block is formed with one or two upper flat deck surfaces against which an overlying cylinder head(s) is bolted. Since both the engine block and head contain oil and coolant passages, a head gasket is interposed between them as a seal to keep the liquids separated as well as seal the cylinder bores.
The engine lubricating oil is a mixture of hydrophobic organic compounds with stabilizing additives, and the coolant is a homogeneous mixture of ethylene or propylene glycol with water and dissolved stabilizing and corrosion-inhibiting additives. The coolant pressure may at times exceed the oil pressure and may leak across the head gasket interfaces into the oil despite the presence of the head gasket.
Proper sealing between the coolant and oiling systems in an engine is of paramount importance to engine durability. Small amounts of coolant contamination in the oil lead to rust and to degradation of oil by removal and decomposition of oil additives. A large amount of coolant contamination can lead to bearing failure due to a loss of bearing load capacity. Significant efforts have been made to design head gaskets that provide durable sealing of the engine cooling system.
Engineers involved in the design or modification of engines need to have a method, other than trial and error, of determining the leakage path of the coolant in order to specify gasket design, bolt location, torque requirements or the like. Techniques that are currently available to measure small rates of coolant leakage are inadequate. Measurement of glycol in oil is only semi-quantitative, and coolant may be lost from the oil by degradation, evaporation or inclusion in engine deposits. Quantitative determination of coolant leakage is possible for coolants that employ potassium salts by measuring the potassium levels in the oil. However, sensitivity is limited because of the relatively small amount of potassium in the coolant. Visual observations can be used inside an engine to determine whether coolant is leaking across a sealed interface. However, the accumulation point may be a distance from the actual leak path, and a fairly high leakage rate is required before it is observable.
In order to provide a means for specifically determining the leakage path across gasket materials, it was decided to determine the feasibility of using radiotracers to detect and locate coolant leakage. An object was to measure precisely where the gasket interface was being breached. In addition, it was a more general object to develop the capability to measure small amounts of coolant contamination in oil.
SUMMARY OF THE INVENTION
In accordance with this invention, a radiotracer method has been developed to measure the presence of small amounts of coolant contamination in oil. Further, a radiotracer method has been developed to determine the pathway(s) of coolant leakage through head gaskets into engine oil.
A radiotracer species was found which would: (i) remain suspended in the coolant during engine operation, (ii) be easily imaged on photographic film, and (iii) be easily detected in engine oil. Results of tests of an engine with known coolant leakage show that the technique can provide images of the leakage path through head gaskets. Also, quantitative values of coolant contamination in oil were obtained with a detection sensitivity better than 50 ppm at 95% confidence.
Several candidate radiotracers were evaluated for their capability to remain suspended in the coolant during engine operation, be easily imaged on photographic film, and be detected in samples of engine oil. The radiotracer selected for engine studies,
86
Rb, was found to perform satisfactorily in each of these areas. For example, rubidium chloride containing a suitable amount of
86
Rb dissolves in water-glycol coolant and because of its radioactivity is detectable both in bulk oil and coolant and with x-ray film laid against a gasket having a suspected leak path.
Results of engine tests such as those described below showed that the
86
Rb tracer is capable of providing quantitative detection of coolant in the oil with a sensitivity better than ±50 ppm at 95% confidence. Images of the distribution of the radioactive coolant in head gaskets were obtained to determine the pathways of coolant leakage into the oil.
Thus, this invention provides a technique to image the pathways of coolant leakage across head gaskets and to provide for the quantitative determination of coolant contamination in lubricating oil. This technique can be used to determine the mechanism of the sealing failures and to evaluate the effectiveness of engineering modifications.
Other objects and advantages of this invention will become more apparent from a detailed description of an embodiment thereof. In the description, reference will be made to the drawings which are as follows.
REFERENCES:
patent: 3745338 (1973-07-01), Joyce
patent: 4746795 (1988-05-01), Stewart et al.
patent: 5968371 (1999-10-01), Verdegan et al.
patent: 2217684 (1974-11-01), None
Blossfeld Daniel Hicks
Gushman Richard William
Schneider Eric West
General Motors Corporation
Grove George A.
Politzer Jay L.
Williams Hezron
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