Measuring and testing – Internal combustion engine or related engine system or... – Compression
Reexamination Certificate
2001-03-19
2003-06-03
McCall, Eric S. (Department: 2855)
Measuring and testing
Internal combustion engine or related engine system or...
Compression
C073S117020
Reexamination Certificate
active
06571615
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a test bed for testing thermal fatigue, in particular for cylinder heads made of light alloy (typically aluminum alloy) for internal combustion engines, and to a method of fatigue testing such cylinder heads.
At present, developing a new cylinder head includes stages of validation on an engine test bed. The typical duration of a conventional test on the test bed is of the order of 800 hours.
In parallel, manufacturers are nowadays designing engines, in particular diesel engines, in which the cylinder heads are subjected to more and more stress, particularly in terms of the ability they must have to tolerate successive starts and stops, both cold and hot, and the ever increasing power that such engines must deliver.
Thus, test campaigns must simulate such working conditions for the cylinder head which means they become lengthier and lengthier, whereas manufacturers are simultaneously requiring that cylinder head development times should become shorter and shorter.
Various test beds exist at present for subjecting cylinders heads to thermal fatigue testing while reducing the time required for testing by reducing the use of tests on an engine test bed. In theory, such beds serve to heat certain zones on the cylinder head that are exposed to the combustion chambers of the engine in a manner that simulates the behavior of the cylinder head when faced with temperature variations that should be similar to those encountered in real operation, but without requiring testing to be performed on an engine test bed.
A first known test bed is designed to apply localized heating to a zone of the cylinder head which is exposed to combustion, and particularly to the inter-seat bridge zones (i.e. between adjacent valve seats), so that these locations reach temperatures close to engine operating temperatures. The burners used are tetrene-oxygen burners.
Nevertheless, that type of testing is performed with a thermal map over the cylinder head as a whole which is very different from that encountered in real operation, so the results obtained are not sufficiently representative. In use, such a test bed is effective in comparing different metallurgical properties (alloys, grain size, . . . ) but not different geometrical properties (in particular the position of the water that cools the tested zone, and the general shape of the cylinder head).
Another known test bed has burners that are supposed to raise those zones of the cylinder head that are exposed to combustion to temperatures that are substantially equivalent to those obtained on an engine test bed. These temperatures are regulated by means of one thermal couple per zone, with the thermocouple determining the temperature reached on the cylinder head. Nevertheless, by its very principle, that method of regulating heating in terms of temperature cannot serve to compare different cylinder head shapes. For example, if the position of the cooling water is changed in such a manner that the cooling of the heated surfaces is improved, then thermocouple regulation has the effect of applying too much heat so that the temperatures continue to reach the reference value, which is no longer representative of the real operating conditions of the engine.
Finally, a drawback of that known test bed lies in that it is incapable of complying with the temperature differences that exist between certain zones of the cylinder head and others, which can significantly affect the representativeness of test results.
Finally, other test beds are known in which cylinder head heating is performed by induction at the valve seat inserts. It will be understood that that type of test bed does not enable a temperature map to be obtained that is representative of the map obtained on an engine test bed.
Thus, none of the known thermal fatigue test beds enable cylinder head development to be accelerated without requiring very frequent testing on an engine test bed. More particularly, although known test beds can be used to validate metallurgical solutions correctly, it is only by using an engine test bed that geometrical solutions can be tested effectively, even though nowadays it is specifically geometrical solutions that are being researched the most since it is geometrical solutions that make it possible to achieve the most significant advances in terms of improving cylinder head lifetimes.
SUMMARY OF THE INVENTION
The invention seeks to mitigate those limitations of the state of the art and to propose a test bed that enables cylinder heads to be subjected to accelerated thermal fatigue testing while obtaining results that are highly representative (mainly detecting thermal fatigue cracks in the inter-seat bridge zone), and to do so in lengths of time that are significantly shorter than prior solutions (typically 40 hours (h) to 200 h as compared with 800 h.
Another object of the present invention is to provide a thermal fatigue test bed suitable for obtaining a temperature map of the exposed zones in the combustion chambers that is very similar to the map obtained on an engine test bed.
Another object of the invention is to be able to compare cylinder heads not only when they have different metallurgical properties, but also when they have different shapes, particularly in terms of the positioning of cooling water.
Thus, the present invention provides a thermal fatigue test bed for an internal combustion engine cylinder head, characterized in that it comprises in combination:
a support for a cylinder head possessing at least one cylinder top zone suitable for being normally exposed to combustion in an engine;
at least one burner suitable for directing a flame onto said zone as a whole; and
at least one heat flux sensor situated in the thickness of said cylinder head in said zone to verify that the heat flux produced by the flame complies at least approximately with a predetermined value.
Preferred but non-limiting features of the test bed of the invention are as follows:
the test bed further comprises a hot cooling liquid circuit and a cold cooling liquid circuit, and means for selectively connecting the cylinder head to one of the two circuits;
the cooling circuits are controlled so as to reproduce at least approximately real conditions of cooling fluid circulation;
each burner is fed with a mixture of saturated hydrocarbon gas and oxygen-enriched air;
the saturated hydrocarbon gas is natural gas;
the test bed further comprises means for adjusting the heat flux supplied by the burners by adjusting the quantities of gas and of oxygen-enriched air in the mixture;
the flux from each burner is adjusted on a respective reference value;
said reference value is selected in such a manner as to generate a temperature map at various points of the cylinder head similar to that obtained under real operating conditions and as measured by means of a cylinder head fitted with temperature sensors;
each burner is suitable for generating a distributed flame capable of producing said temperature map in the associated cylinder top zone;
each burner possesses a perforated plate having a predetermined distribution of orifices;
said distribution is non-uniform; and
each heat flux sensor is mounted at the end of a fuel injector suitable for mounting in the cylinder head, said end being adapted to receive said sensor.
In a second aspect, the invention provides a method of calibrating a thermal fatigue test bed for internal combustion engine cylinder heads, the method being characterized in that it comprises the following steps:
providing a set of temperature sensors in a cylinder head fitted with instruments, said sensors being in the vicinity of at least one zone that is to be exposed to engine combustion;
using the temperature sensors while the cylinder head is in operation on an engine test bed to determine a temperature map for said zone under steady conditions;
storing said temperature map;
mounting a heat flux sensor in said zone of the cylinder head fitted with instruments;
placing the cylinder head fitted with instruments on a therm
Dupain Arnauld
Guimbal Frédéric
Meyer Philippe
Blakely & Sokoloff, Taylor & Zafman
McCall Eric S.
Montupet S.A.
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