METHOD OF LOCATING FRICTION GENERATING DEFECTS IN A MULTIPLE BEARING ASSEMBLY

Abstract: A method of determining the location and type of dimensional defects, particularly friction generating defects, which comprises: (a) initiating simulated operation at ambient conditions of an assembly (10) having certain sliding or rolling contact surfaces; (b) sensing (25) any change in the temperature of such assembly surrounding each certain sliding or rolling contact surfaces (i) with a resolution of .02-1.0°C (preferably .1-.7°C) and (ii) during a time span of 2-10 seconds measured from such initiation to provide separated voltage signals for each location; (c) converting the signals to a digitised thermal map (32) ; and (d) comparing (34) the sensed digitised thermal map with a reference digitised thermal map for such an assembly without defects operated during the same time span and adjusted to compensate for any differing thermal conditions. Any deviations detected by such comparison representing defects.

Description: Field of the invention This invention relates to the art of sensing operational defects in piston and bearing assemblies and, more particularly, to sensing such defects at sliding and rolling contact areas of an engine. Background of the invention It is conventional in the automotive industry to test a newly assembled engine by a simple screening process to identify engine assemblies that bind. A torque transducer is placed between an engine assembly output member and a drive motor; the motor essentially drives the mechanical elements of the engine assembly in a non-firing condition. This is a cumulative sensing technique because it is possible that some parts may be too loose and some too tight; the total torque may mask the problem of the overly tight parts which may be close to binding. This technique does not locate the source of friction causing defects, it merely renders a consensus that there may be a problem somewhere in the engine assembly without identifying the location. Additionally, such torque transducer tests may permit burrs to gouge out an annular groove on the first turn of the test, permitting the torque to go back down to normal without revealing a permanent defect. If any defect is discovered by the torque transducer test, the engine must be withdrawn from the assembly line, disassembled, and explored as to location of possible problems. This is time-consuming , not always accurate. If the friction causing defect has become permanent as a result of scratching or binding and has been discovered, this will eventually require rework or scraping of the sliding or rolling bearing surfaces. If the friction causing defect has not been discovered because permanent grooving has taken place, the engine in regular use may, depending on the location of the defect, experience knocking, loss of oil pressure, seizure of crankshaft, or premature engine failure. To fix such defect in the field may cost 40 times what it would cost to fix the defect at the assembly line. Similarly, dynamometer devices which sense an accumulation of delicate engine parameters while the engine is running hot are not useful to screen out friction causing defects because the sensing will be too late after damage has become permanent (see U.S. patent 3,592,053). It would be desirable if dimensional or friction generating defects in newly assembled engines could be sensed by a technique that locates the defect in an extremely short time period, before the defect can damage the sliding or rolling surfaces and particularly before a friction binding part can penetrate the assembly oil film at such contact areas. It would further be desirable if radiation from such dimensional defects could be sensed sufficiently quickly and accurately to determine location and type of such defects before such damage can occur. Heat sensors, such as those permanently incorporated in a rotary engine (see U.S. patent 3,886,912) or valve body (see U.S. patent 3,921,435) to sense binding, are inappropriate for detection use in multiple bearing or piston assemblies such as a complex internal combustion engine; a large number of sensors, such as 15 or more, would have to be incorporated, increasing the cost and complexity. Infrared radiation cameras have been used to monitor the heat pattern, on a gross or macro scale, of large storage tanks or containers, such heat pattern having been in existence for some time at a desirably constant level. A change in the heat pattern would signal the possibility of a lining breakthrough (see U.S. patents 4,343,182 and 3,596,519). Thermographic techniques have also been proposed to identify defects in mechanical products (MACHINE DESIGN, vol. 55, no. 25, November 1983, page 54-58, Cleveland, Ohio, USA, C. C. Roberts, "Troubleshooting products by infrared thermography". For example, a misaligned universal joint will run hot and the observed thermal pattern can pin point the problem. FR-A-2,186,137 describes an application for thermography in the examination of items such as printed circuit boards which have a large number of elements each emitting different intensities of infrared radiation. EP-A-0 084 374 discloses techniques of image processing and display for use in thermography which allow the image of an article to be compared point by point with a stored image in order to reveal differences. Even though thermography is known in itself, the use of radiation cameras in the limited manner described in the prior art does not offer a solution to the problem of identifying defects in an internal combustion engine during its assembly, before damage is caused to the sliding or rolling surfaces and particularly before damage can occur as a result of penetrating the assembly oil film present throughout the engine. The time period in which this can occur is less than 15 seconds. Object of the invention The invention therefore seeks to provide a method of detecting operational defects in piston and bearing assemblies of an engine and, more particularly, to sensing such defects at sliding and rolling contact areas, in order to prevent damage to the engine from such defects. Summary of the invention According to the present invention, there is provided a method of sensing operational defects at sliding or rolling contact areas of a combustion engine assembly, which comprises the steps of : a) initiating turning of the engine assembly at around 750 r.p.m. at ambient temperature without igniting a fuel mixture in the cylinders, which turning is herein referred to as motoring of the engine assembly, and discontinuing the motoring after a period of 2 to 10 seconds, b) sensing, by the use of infrared thermography and with a resolving power of .02-1.0°C, any change in the temperature of said engine assembly in the vicinity of the sliding or rolling contact surfaces during motoring of the engine assembly, to provide voltage signals indicative of the temperature at different locations in the engine assembly, (c) digitising said signals; and (d) comparing the digitised signals with digitised reference signals which are derived from an engine assembly without defects motored for the same period of time and are adjusted to compensate for any differing ambient thermal conditions, any deviations detected by such comparison representing defects. The invention is predicated on important discoveries. First, the heat generation after only about two seconds of engine motoring is transmittable and can be detected by infrared thermography. Second, the friction causing defects usually do not cause damage or penetrate the assembly oil film at a rolling or sliding contact surface in a time span of less than 10 seconds. Consequently, by motoring for a short time, one can obtain enough information to locate the defects before there is a serious risk of the defects causing damage to the engine. The term motoring is used herein to mean turning the engine assembly, at ambient temperature conditions without fuel mixture combustion taking place, at around 750 r.p.m.. The turning speed should be set as low a speed as possible consistent with temperature data being produced that can be sensed within the desired time span of 2 to 10 seconds. Temperature sensing is carried out by the use of infrared thermography which may use one of the following types of equipment, namely thermal camera, radiometer, and thermal line scanner. The term temperature resolution as used herein refers to the smallest threshold unit of perception of a change in temperature detected by a thermal sensing unit. Advantageously, one to three cameras may be deployed to scan a complex assembly with some of such cameras being eliminated by the use of mirrors. To eliminate interference from background lighting, the assembly may conveniently be placed in a black box. Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which : Figure 1 is a basic flow diagram of the method steps of this invention, and Figure 1A is an amplified flow diagram of the preferred process; Figure 2 is a perspective view of a cut-away engine assembly to illustrate location of sliding or rolling contact areas; Figure 3 is a schematic diagram of an apparatus layout used to carry out the method of this invention; Figure 4 is an alternative engine head sub-assembly viewed from an angled perspective; and Figure 5 is a computer generated thermal map produced in accordance with this invention and depicting a defect in No. 4 cylinder bore. Description of the preferred embodiment A preferred method mode is set forth in the expanded flow diagram of Figure 1A. The engine sub-assembly consists of a cylinder block and crankcase with associated moving parts installed therein, such as pistons with piston rings, connecting rods and rod bearings, crankshaft and main bearings. It is possible to test the entire engine as fully assembled, as shown in Figure 2, but certain areas of concern will be masked and interrupt a clear line of sight to the thermal sensor unless complex mirrors are used. As shown in Figure 2, areas of concern for the cylinder block and crankcase sub-assembly 10 are (i) the fit between the piston 11 and piston rings 12 to the cylinder bore 13 which represent first sliding contact surfaces, (ii) the rolling contact fit between the bearing sleeves in the big end 14 of the connecting rod and the crank arm 15 of the crankshaft 16, and (iii) the rolling contact fit between the main bearings at each bulkhead of the crankcase 18 and the main shaft 19 of the crankshaft 16. In a head assembly, the areas of concern are (i) the rolling contact fit between bearings 20 for the camshaft 21 and the camshaft itself, (ii) the sliding fit between the valve stem 22 and the valve guides 23, and (iii) the action of the valve springs 24. Simulated Operation The output shaft 29 of the crankshaft 19 of sub-assembly 10 is connected to an electric drive motor 10, as shown in Figure 3. The movable parts of the sub-assembly are motored or driven without firing (combustion in the cylinder bore) and at ambient temperature conditions. The cylinder block-crankcase sub-assembly is shown with its bottom up, having the main bearings 17 for the crankshaft on top, and the bearings for the connecting rod big end 14 exposed therebetween. The fit between the piston and cylinder bore is underneath, but can be viewed from a side elevation viewpoint. The crankshaft is turned at a speed of about 750 r.p.m. As shown schematically in Figure 4, the sub-assembly of only the engine head 28 and its associated moving parts may be subjected to simulated operation. The input member (camshaft 21) is connected to an electric drive motor for operation at intended speeds for such member. The front of the camshaft bearings 20 can be viewed from a perspective as illustrated in Figure 4 and the rear of the bearings 20 can be viewed by use of one or more mirrors 31. Out of dimension defects can occur in the cylinder block-crankcase sub-assembly by the fit of the piston being undersized, oversized, or the piston rings folded out of position either in or out of the piston grooves or missing piston rings. A condition of oversize can occur by installation of a piston into a cylinder bore that reduces the piston to bore clearance beyond the minimum permitted. For example, in a typical 1.9L engine, the acceptable range of piston to bore clearance is .0012-.0020 inches (clearance is the total diametrical difference). If such clearance is reduced below the minimum by an oversized piston, the thermal camera will detect such. With a thermal camera having a resolution power of .5°C, an oversize defect of as little as .0005 inch can be detected in 10 seconds when compared to a non-defect reference. Similarly, if the maximum clearance is exceeded by an undersized piston for the bore, sufficient thermal emission differences can be detected in 10 seconds of motoring at .5°C resolution power to locate the defect and type it as undersize. Piston oversize or undersize can occur as a result of machining control or dimensional damage after machining or grading. In the assembly of piston to cylinder bores, it is conventional to grade the pistons and cylinders into A through F categories, each differing by .0004 inches; accordingly, different grades of pistons are matched with different cylinder bores to meet the clearance tolerance range, such as .0012-.0020 inches. This invention locates and types dimensional aberrations that exceed such range even after such matching is carefully conducted during assembly. In automotive main bearings for the crankshaft, it is typical to design in a clearance tolerance of .0008-.0026 inches (.020-.065 mm) and similarly for connecting rod bearings, it is typical to design in the same clearance. Deviations beyond this range of as little as .001 inch can easily be detected by a thermal sensor with a resolution power of .5°C during a motoring time span of 10 seconds or less. Sensing and Thermal Mapping As shown in Figure 3, a thermal camera 25 is directed at the automotive engine sub-assembly to sense infrared radiation during a time span of 2-10 seconds measured from the initiation of the motoring. The camera may be positioned generally in the same horizontal plane that passes through the bearings for the crankshaft and preferably is directed slightly downwardly at an angle of about 30° with respect to such plane to have a line-of-sight to the entire annular character of the piston rings. The camera or sensing mechanism may be selected from one of the following: a thermal camera, a radiometer, and a thermal line scanner. Preferably, an infrared thermal camera is employed for carrying out the preferred mode herein, such camera having a field of view which encompasses both ends of the subassembly and a depth of field which can encompass the front and back of the sub-assembly. The sensing mechanism can have a resolution power that can distinguish changes in infrared radiation corresponding to .02-1.0°C, but sensitivity within the range of .1-.7°C is best because it does not generate false signals. A thermal camera with resolution power of .1-.7°C will be able to distinguish a spectrum of at least eight colons for colour prints or at least eight gradations of grey for computer imaging. To more effectively sense infrared radiation, a plurality of thermal cameras may be employed which, of course, adds to the expense of the apparatus; this may be reduced by employing mirrors 27 to substitute for the additional cameras, permitting viewing of the back side of bearings along a line of sight 26 as shown in Figure 3. The output from the thermal camera or imaging will be voltage signals corresponding to the location in the scan of the camera and as a function of time. These signals are received by a monitor 32 and are converted to a digitised signal by digitiser 33. The output of the digitiser is connected to a computer 34 which manipulates the digitised signal. Such computer should have a capacity sufficient to receive rapid signal sensations which may result from the thermal camera being run at a range of 20-35 frames per second. The output of computer 34 can be selectively directed to a video recorder 35 (which provides for a thermal map imaging), a printer 36, or recorded in Polaroid film by an instant-type camera 37. To more effectively eliminate any interference, such as from fluorescent lighting that may be in the test room, the engine is placed in a black box 41. The sensed digitised signals are compared to reference digitised signals for the same sub-assembly that is known to have no defects. Thermal mapping comparison will thus allow the tester to determine where a defect exists and what type of defect, i.e., whether oversize or undersize. The reference digitised signals must be adjusted to compensate for any differing ambient thermal conditions. The computer techniques to implement the method steps of this invention are known to those skilled in the art. Figure 5 shows a computer generated thermal map for a cylinder block sub-assembly with the thermal camera pointed directly down onto the open cylinder bores. Cylinder bore #4 (which is circled) shows a graded image that corresponds to an excess temperature (23.9-24.2°C) beyond the predetermined permissible temperature range of up to 24.0°C; this imaging occurred after eight seconds of motoring. While particular embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention as defined in the appended claims. For example, the thermal camera viewing angle may be varied from that shown in Figures 3 and 4. The camera may be placed directly over the top of the cylinder block in an upright position, using mirrors to receive thermal emissions from underneath the block.

Claims: A method of sensing operational defects at sliding or rolling contact areas of a combustion engine assembly, which comprises the combustion steps of : a) initiating turning of the engine assembly at around 750 r.p.m. at ambient temperature without igniting a fuel mixture in the cylinders, which turning is herein referred to as motoring of the engine assembly, and discontinuing the motoring after a period of 2 to 10 seconds, b) sensing, by the use of infrared thermography and with a resolving power of .02-1.0°C, any change in the temperature of said engine assembly in the vicinity of the sliding or rolling contact surfaces during motoring of the engine assembly, to provide voltage signals indicative of the temperature at different locations in the engine assembly, (c) digitising said signals; and (d) comparing the digitised signals with digitised reference signals which are derived from an engine assembly without defects motored for the same period of time and are adjusted to compensate for any differing ambient thermal conditions, any deviations detected by such comparison representing defects. A method as claimed in claim 1, in which infrared thermography is carried out by use of a device selected from the group consisting of a thermal camera, a radiometer, and a thermal line scanner. A method as claimed in claim 1 or 2, in which in step (c) said signal is converted to a digitised thermal map and the comparison in step (d) is carried out with a reference digitised thermal map. A method as claimed in any one of the preceding claims, in which the resolving power of step (b) is in the range from 0.1°C to 0.7°C. A method as claimed in claim 1, in which said thermal sensing is carried out by use of a single thermal camera and by use of a plurality of mirrors at remote locations about said assembly to sense infrared radiation in the engine assembly, not in the direct line of sight of the camera. A method as claimed in claim 1, in which said scanning is carried out by the use of a plurality of thermal cameras. A method as claimed in claim 1, in which said sensing is carried out with the engine assembly protected by a black chamber to eliminate radiation interference.

Inventors: YERACE, DANIEL, ZINKOSKY, ALEXANDER JULIUS
Applicants: FORD FRANCE S. A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1989
Main classification: G01N25
IPC codes: G01M19, G01N19, G01M13