GB2360363A

GB2360363A - Thermal fatigue testing of engine components

Info

Publication number: GB2360363A
Application number: GB0102370A
Authority: GB
Inventors: Al R Lecz; Edward Akpan; Mark Merwin Griffith; John Lasecki; Ronald H Hasenbusch
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2000-03-16
Filing date: 2001-01-31
Publication date: 2001-09-19
Also published as: GB0102370D0

Abstract

An apparatus for thermal fatigue testing an engine component eg. cylinder head 12 that is normally subjected to thermal cycling includes a fixture 13 for supporting the component in a manner which simulates the engine-mounted condition, including the cooling effects generated by circulation within the engine of a coolant, as through delivery of a coolant through the fixture. A gas burner 34 is provided for selectively generating a hot gas stream, preferably for direct impingement upon the engine component, whereby the temperature of a targeted surface or structure of the component may be raised to an upper target temperature. The apparatus also includes at least one temperature sensor (56, fig.2) whose output signal is correlated with a temperature of one of the component's surfaces or structures; and a controller 52 which, responsive to temperature signal, is adapted to selectively operate the burners and to circulate coolant to thereby thermally cycle the component between at least one pair of upper and lower target temperatures.

Description

2360363 TESTING APPARATUS FOR ENGINE COMPONENTS AND OPERATING METHOD The

invention relates to apparatus and methods f or the s testing of cylinder heads and other components used in or on modern internal combustion engines and which are subjected, during the engine's service life, to stresses incident to thermal cycling.

The prior art has acknowledged that certain components disposed in thermally high-stressed and strongly-heated regions of an internal combustion engine, such as its cylinder heads, are subject to differential heat stressing as a result of direct contact between the components and the is hot combustion gases. Such differential heat stressing of localised portions of such components has been known to reduce the service life of some components and, hence, of the engine due to thermo-mechanical fatigue. Stated another way, by way of example only, a cylinder head may be expected to experience greater then perhaps 20,000 thermal cycles during the engine's normal service.

In an attempt to solve this problem, internal cooling channels are provided in the thermally highly-stressed parts or regions of many internal combustion engines. During normal engine operation, a suitable cooling medium such as water or a mixture of water and ethylene glycol is circulated both through the thermally highly- stressed parts or regions and a suitable heat exchanger, such as a radiator. In this manner, the temperatures in certain critical regions of the engine are substantially reduced. Unfortunately, such local temperature reductions may correlatively generate even greater thermal gradients with respect to any remaining "hot spots," resulting in increased risk of thermal-stress-induced fatigue. Thus, new and improved component designs, many featuring different materials and fabrication methods, are being developed which are less likely to generate "hot spots" or are otherwise less susceptible to thermal fatigue.

It is desirable to validate such new component designs through durability testing before placing the components into regular production. Because the service life of an engine may exceed many years, such validation testing preferably simulates the engine service environment at an accelerated pace.

Thus, the prior art teaches a first apparatus and method for durability testing an engine component, such as a cylinder head, in which the cylinder head is mounted in a fixture such that each combustion chamber cavity defined in the cylinder head lies within the effluent streams of both a gas-fired burner and a water-quenching spray nozzle. Hot gases and cold water alternately impinge upon localised surfaces of the cylinder head, including the web or bridge defined between the inlet and outlet valves of each combustion chamber cavity, at a rate of perhaps about 30 to 40 cycles per hour. Using this first prior art approach, a thermal fatigue failure of an engine component can be rapidly induced in perhaps as few as 100 to 200 cycles. Unfortunately, the temperatures to which the component is subjected during the first method cannot be accurately controlled. in part due to temperature increases in the water that is recirculated through the spray nozzles, and the fact that the impinging water stream is unable to accurately control the localised temperatures of relativelyfine cylinder head features, such as its exhaust radii, its deflectors, and its valve bridges.

Alternatively, the prior art teaches a second apparatus and method for durability testing engine components wherein an assembled engine is operated on a dynamometer. Under this second prior art approach, the assembled engine is operated in such a manner as to simulate the engine's normal thermal characteristics throughout its service life, perhaps aided by a test profile or thermal history which has previously been obtained for the particular test engine.

Unfortunately, the thermal mass and other characteristics of the assembled engine combine to require thermal cycles of much greater length in order to subject the subject component to the desired temperature extremes.

Indeed, to the extent that the failure of another engine component does not otherwise terminate such dynamometer testing of the subject component, it is been suggested that perhaps in excess of 20,000 to 30,000 thermal cycles might be required to induce a fatigue failure due to thermallyinduced stresses. Moreover, it will be appreciated that it is is difficult to obtain direct temperature readings with respect to localised regions, e.g., the valve bridge, of an installed cylinder head. Instead, the second prior art approach relies upon exhaust gas temperature as an indirect measure of the temperature of the cylinder head surfaces and/or structures upon which hot combustion gases impinge during engine operation. Such indirect temperature measurement of critical component surfaces and/or structures necessarily reduces the accuracy and reliability of such dynamometer tests.

According to the present invention, there is provided an apparatus for fatigue testing a component of an internal combustion engine having a first localised portion that is subjected to differential heat stressing during the service life of the engine, the apparatus including:

a fixture for supporting the component, wherein a portion of the fixture defines at least a first part of a first fluid-tight passage; a coolant supply operative to deliver a coolant under pressure to the first internal passage of the fixture, whereby a temperature of the localised portion-of the component is lowered; a burner operative to generate hot exhaust gas for impingement on at least the first localised portion of the component; a sensor generating a signal correlated with a temperature of the localised portion of the component; and a controller adapted to selectively operate the burner and the coolant supply to repeatedly cycle the localised portion of the component between a lower target temperature and an upper target temperature.

Claims

In accordance with a second aspect of the present invention there is

provided an apparatus for the thermalfatigue testing of a component as hereinafter set forth in Claim 10 of the appended claims.

In accordance with a further aspect of the invention, there is provided a method of testing a component as hereinafter set forth in Claim 16 of the appended claims.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic schematic view of an exemplary thermalfatigue testing apparatus in accordance with the invention; and Figure 2 is an enlarged, diagrammatic, partial crosssection of a cylinder head secured to the exemplary apparatus shown in Figure 1.

Referring to Figure 1, an exemplary apparatus 10 for performing accelerated thermal-fatigue/durability testing of a component, such as a pair of aluminium cylinder heads 12, of a gasoline -powered internal combustion engine (not shown) includes a fixture 13 formed from a cylinder block 14 mounted on a back plate 16, preferably such that the cylinder 18 defined within the cylinder block 14 extends at least somewhat vertically to thereby facilitate drainage of quenching fluid, as discussed further below. The deck 15 of each of the cylinder block's banks thereby defines a mounting platform to which each cylinder head 12 can be suitably secured, as by fasteners (not shown).

The apparatus 10 further includes a closed-loop coolant supply 20 for supplying a suitable cooling fluid to the water jackets of the cylinder block 14 and each cylinder head 12, respectively, once the cylinder head 12 is suitably mounted atop its respective cylinder bank. While the invention contemplates use of any suitable coolant supply 20, in the exemplary apparatus 10, the coolant supply 20 includes a coolant reservoir 22; a pump 24 operative to circulate cooling fluid from within the coolant reservoir 22 into the water jackets; a heat exchanger 26 connected to a suitable supply of relatively-cooler fluid, such as a water line; a pressure control device 28, and associated supply and return conduits 30,32. A coolant temperature control device, such as a thermostat 32, is situated in the supply conduit 30 to facilitate coolant temperature regulation.

As seen in Figure 1, the exemplary apparatus 10 further includes a burner 34 extending into each cylinder 18 defined within the cylinder block 14, preferably, toward the geometric centre of the combustion chamber. The burner 34 is operative to generate hot exhaust gases which are directed onto various surfaces and/or structures on the subject cylinder head 12, such as the cylinder head's valve bridge. Preferably, the temperature of the impinging exhaust gases can be varied between about 500C and about 2500C to thereby simulate a range of engine operating conditions, and to otherwise provide variable heating rates to thereby approximate the heating rate experienced by the cylinder head 12 during such normal engine operating conditions as engine start-up and during the period after engine shutdown. The precise location of each burner 34 within its respective cylinder 18 and/or the burner's relative output can also be adjusted to provide an desired temperature variation between the various cylinders 18. The burner 34 is preferably operated at a stoichiometric airfuel ratio to reduce carbon deposits on the cylinder head 5 12.

The exemplary apparatus 10 further includes a quenching fluid supply 36 having a reservoir 38 containing a quantity of the quenching fluid; at least one nozzle 40 extending into each of the block's cylinders 18; a pump 42 operative to supply quenching fluid at a desired pressure and rate to the nozzles 40; a quenching fluid collector 44 positioned beneath the cylinder block 14; a heat exchanger 46 connected to a suitable supply of relativelycooler fluid, such as a water line; and associated supply and return conduits 48,50.

While the nozzles 40 may be aimed such that the quenching streams impinge upon any appropriate surfaces or structures of the cylinder head 12, including any previously-identified "hot spots," in the exemplary apparatus 10, each nozzle 40 is aimed such that the quenching stream impinges upon the valve bridge of a two-valve cylinder head, or on the geometric centre of the combustion chamber of a three- or four-valve cylinder head. A coolant -temperature controller 51 is also situated in the supply conduit 48 of the quenching fluid supply 36 to facilitate temperature regulation of the quenching fluid.

Finally, the exemplary apparatus 10 includes a controller 52 which selectively operates, for example, the cooling supply pump 24, the burners 34, and the quenching fluid supply pump 42, in response to the detected or determined temperature of at least one surface or structure of the cylinder head 12, such that detected or determined temperature is repeatedly cycled between at least one predetermined lower target temperature and at least one predetermined upper target temperature.

7 - Figure 2 is an enlarged, diagrammatic, partial crosssection of the cylinder block 14 showing the attached cylinder head 12. As seen in Figure 2, a head gasket 53 is positioned between each cylinder head 12 and its respective bank 54 atop the cylinder block 14 to further assist in simulating the operating environment of the cylinder head 12 and, particularly, the thermal loads to be applied to the cylinder head 12 during repeated thermal cycling of the engine. While the invention contemplates use of any suitable apparatus or methods for monitoring the local temperature of one or more surfaces and/or structures of the cylinder head 12 during a given test, in the exemplary apparatus 10, a temperature sensor 56 inserted in each spark plug aperture 58 of the cylinder head 12, preferably through use of a mapped correlation between the sensor outputs and those surfaces and/or structures. By way of further example, a thermocouple (not shown) may alternatively be imbedded in epoxy on a suitable cylinder head structure, such as the valve bridge, with the spark plug apertures 58 otherwise suitably closed off. Each cylinder head 12 is mounted atop its respective bank 54 of the cylinder block 14 with fasteners (not shown) which are themselves preferably tightened to the same degree as would be achieved when mounting the cylinder head 12 on the cylinder block 14 for normal engine operation.

In accordance with the invention, a test of the subject cylinder heads 12 generally comprises the temperature cycling of a targeted surface or structure of one or both of the cylinder heads 12 between an upper target temperature and a lower target temperature with a typical cycle time in the range of between about two minutes and five minutes. Each cycle is keyed to variation of the temperature of the cylinder head between desired minimum and maximum temperature targets, as directly detected by or otherwise inferred from the output of the temperature sensor 56.

Thus, in operation, when the detected or determined temperature of the cylinder head 12 is lower than the lower target temperature, the controller 52 initiates a heating phase by igniting and otherwise operating the burners 34 in a manner such that the temperature of each cylinder head's targeted surface or structure is raised at a desired rate to the upper target temperature. Upon achieving the upper target temperature, the controller 52 initiates a cooling phase by extinguishing or otherwise returning the burners 34 to a pilot flame, whereupon the controller 52 operates the coolant supply pump 24 to deliver coolant through the respective water jackets 60,62 of the cylinder block 14 and the cylinder heads 12 (as seen in Figure 2), possibly with the further aid of an impinging quenching stream upon operation of the quenching fluid supply pump 42 under the control of the controller 52. The respective heat exchangers 26,46 and temperature controllers 32,51 of the coolant supply 20 and quenching fluid supply 36 otherwise act to control the temperatures of the respective fluids.

Under a first variation of the above operating method, the coolant is continually circulated through the water jackets of the cylinder block 14 and the cylinder heads 12.

In this manner, heat is generally swept away as soon as it is generated, thereby quickening the pace of the test.

Under the first variation, the controller 52 simulates the temperature rise normally experienced by the cylinder head 12 immediately upon engine shutdown by continuing to operate the burners 34 for a predetermined period after the upper target temperature has been reached.

Under a second variation of the above operating method, the controller 52 simulates the temperature rise upon engine shutdown by extinguishing or reducing the burner flame and, significantly, by temporarily interrupting circulation of. the coolant through the cylinder block 14 and the cylinder 9 - heads 12 for a predetermined time period, once the cylinder head 12 has reached the upper target temperature.

In accordance with another feature of the invention, the thermal cycling of the cylinder heads 12 on the apparatus 10 is itself preferably periodically interrupted after a predetermined number of cycles, for example, between about 100 and 150 cycles, to facilitate crack mapping of the cylinder heads 12. However, when greater accuracy is desired, as when performing a comparative test on two competing cylinder head designs, one atop each respective bank of the apparatus's cylinder block 14, the invention contemplates stopping the thermal cycling after completion of a smaller number of cycles, for example, fewer than is thirty cycles.

While an exemplary system and associated operating methods have been illustrated and described, it should be appreciated that the invention is susceptible of modification without departing from the scope of the invention as set forth in the appended claims. For example, while the exemplary apparatus 10 advantageously employs a test fixture which includes an actual engine block to thereby properly simulate thermal operating stresses on the subject cylinder head 12, the invention contemplates use of another suitable supporting fixtures including, for example, a generally-planar mounting plate which defines, on a first surface thereof, an interchangeable fixture adapted to receive the deck face of the cylinder head 12. Such a mounting plate will include a plurality of larger apertures intersecting the first surface which are substantially aligned with the combustion chamber cavities defined in the cylinder head 12, through which appropriate burners may be extended. The mounting plate would also preferably include additional threaded apertures adapted to receive fasteners that are inserted through corresponding mounting holes formed in the cylinder head, whereby the cylinder head is drawn against and secured to the first face of the mounting plate in a manner similar to that by which the cylinder head is normally mounted atop the engine's cylinder block.

Similarly, while the exemplary apparatus 10 has been described in connection with the testing of a cylinder head 12, it will be appreciated that the invention is suitable for evaluating the service performance of myriad engine components, including but not limited to sensors, coolant mixes, and gasket materials.

CLAIMS 1. An apparatus for fatigue testing a component of an internal combustion engine having a first localised portion that is subjected to differential heat stressing during the service life of the engine, the apparatus including:

a fixture for supporting the component, wherein a portion of the fixture defines at least a first part of a first fluid-tight passage; a coolant supply operative to deliver a coolant under pressure to the first internal passage of the fixture, whereby a temperature of the localised portion of the component is lowered; a burner operative to generate hot exhaust gas for impingement on at least the first localised portion of the component; a sensor generating a signal correlated with a temperature of the localised portion of the component; and a controller adapted to selectively operate the burner and the coolant supply to repeatedly cycle the localised portion of the component between a lower target temperature and an upper target temperature.
2. An apparatus as claimed in claim 1, wherein a surface of the localised portion of the component defines a second part of the first passage.
3. An apparatus as claimed in claim 1, wherein the fixture includes a second passage providing direct access to the localised portion.
4. An apparatus as claimed in claim 3, wherein the burner is positioned within the second passage of the fixture.
5. An apparatus as claimed in claim 3 or 4, further including a quenching fluid supply operative to deliver a quenching fluid under pressure into the second passage of the fixture.
6. An apparatus as claimed in any preceding claim, wherein the coolant supply is a closed-loop system having a coolant reservoir, a pump, and a temperature controller.
7. An apparatus as claimed in any preceding claim, further including a supply of a heat-exchanging fluid, and lo wherein the coolant supply further includes a heat exchanger operative to transfer heat from the coolant to the heatexchanging fluid.
8. An apparatus as claimed in any preceding claim, wherein the signal represents a temperature of the localised portion of the component.
9. An apparatus as claimed in claim 8, wherein the sensor directly detects the temperature of the localised portion of the component.
10. An apparatus for the thermalfatigue testing of a component adapted for installation in or on an internal combustion engine, wherein a localised portion of the installed component is subjected to differential heat stressing during engine operation, the apparatus comprising:

a gas burner selectively operative to generate hot exhaust gas; a fixture for supporting the component such that the localised portion of the component receives the hot exhaust gas; a cooling system selectively operative to deliver a cooling fluid into thermal contact with the component; a sensor generating a signal correlated with a temperature of the localised portion; and a controller responsive to the signal for selectively operating the gas burner and the cooling system to alternately heat and cool the localised portion of the component between an upper target temperature and a lower target temperature.
11. An apparatus as claimed in claim 10, wherein the component includes a cooling passage extending proximate to the localised portion of the component; and wherein the cooling system delivers the cooling fluid under pressure to the cooling passage.
12. An apparatus as claimed in claim 10 or 11, wherein the cooling fluid makes direct thermal contact with the localised portion of the component.

is
13. An apparatus as claimed in claim 12, wherein the cooling system includes a nozzle positioned proximate to the localised portion of the component such that cooling fluid from the nozzle impinges directly upon the localised portion of the component.
14. An apparatus as claimed in any of claims 10 to 13, wherein at least one of the upper and lower target temperatures varies over time.
15. An apparatus as claimed in any of claims 10 to 14, wherein the cooling system includes a heat exchanger operative to transfer heat from the cooling fluid to a heat exchanging fluid.
16. A method of testing a component adapted for installation in or on an internal combustion engine, wherein a localised portion of the installed component is subjected to differential heat stressing during engine operation, the apparatus comprising:

mounting the component on a fixture; generating a signal correlated with a temperature of the localised portion; - 14 selectively directing a hot exhaust gas into thermal contact with the localised portion of the component based on the signal; and selectively directing a first cooling fluid into thermal contact with the component based on the signal, such that the temperature of the localised portion of the component repeatedly cycles between an upper target temperature and a lower target temperature.
17. A method as claimed in claim 16, wherein the first cooling fluid makes thermal contact with a portion of the component other than the localised portion of the component.
18. A method as claimed in claim 16, wherein directing the first cooling fluid includes supplying the cooling fluid under pressure to a cooling passage formed in at least one of the fixture or the component.
19. A method as claimed in claim 18, wherein selectively directing the cooling fluid includes interrupting the supply of cooling fluid when the temperature of the localized portion of the component exceeds the upper target temperature.
20. A method as claimed in claim 16, further including directing a second cooling fluid into thermal contact with the localized portion of the component.
21. A method as claimed in claim 16, further including varying at least one of the upper and lower target temperatures over time.
22. An apparatus for fatigue testing a component of an internal combustion engine, substantially as herein described with reference to and as illustrated in the accompanying drawings.