Abstract:
A system and method for determining the condition of lubricating oil in an oil-utilizing mechanism, said system comprising: sensor means for sensing the chemical composition of oil vapor in the head space of the oil reservoir, or a holding reservoir; temperature probes for sensing the temperature of the oil and of the sensor means; microprocessor means connected to the sensor means and temperature probes for creating a vapor signature by means of a pattern recognition algorithm representing the chemical composition of the vapor in the head space; and display means for producing a discernable indication to an operator if the processor means determines that the vapor signature deviates from predetermined baseline parameters. The system is initiated when the oil-utilizing mechanism is shut off, or when a sample of oil is taken from the oil reservoir and placed in the holding reservoir, and senses conditions periodically during cool-down of the oil.

Description:
The present application is a continuation-in-part of co-pending U.S. patent application Ser. No. 09/192,707, filed on Nov. 16, 1998, now U.S. Pat. No. 6,128,561. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a self-diagnostic system for determining maintenance conditions of lubricants in oil-utilizing machines operating under intermittent loads. More particularly, the present invention relates to a system and method for determining the condition of oil in an engine, transmission, or the like, in order to optimize oil maintenance intervals. 
     2. State of the Art 
     Lubricating oils are typically comprised of high molecular-weight products of the petroleum distillation process. The base constituents of these oils are typically hydrocarbon chains having anywhere from 16 to 30 carbon atoms, and a boiling point higher than 350° C. Undesired constituents such as tars, asphalts, greases, and paraffin waxes are preferably removed during the refining process, and certain additives such as thickening agents, detergents, and anti-oxidants may be added to impart desired properties to the oil. 
     As oil is used in the high temperature, high stress environment of an internal combustion engine or other oil-utilizing machine, the base hydrocarbons tend to break down over time. Typically, the relatively long hydrocarbon chains of the base oil break up and degrade into oxidized forms of hydrocarbons such as polyacohols, aldehydes, carboxylic acids, esters, etc., which have inadequate or undesirable properties. When some significant proportion of the base oil has broken down in this way, the oil will no longer protect the machine from damage as desired. 
     At present, oil changes in internal combustion engines and similar oil-utilizing machines are typically performed according to the mileage or hours of operation of the machine, not according to the directly identified needs given by the chemical state of the lubricating oil. However, it will be appreciated that the miles driven or hours of use do not necessarily indicate the condition of the oil. For example, operation under heavy or rapidly varying loads, or under dusty or extreme temperature conditions will tend to cause oil to break down sooner than otherwise. A mileage or time-based schedule is thus only an approximation of the actual needs, based on numerous assumptions. The result is that the lubricating oil may be changed too infrequently, resulting in accumulated damage to the mechanical parts, or it may be changed more often than needed, causing needless maintenance expense and producing excessive waste oil. While one could periodically remove a sample of oil from a vehicle&#39;s oil reservoir and have it chemically tested, this is so time consuming, expensive, and inconvenient as to be essentially impractical. 
     It would be desirable to have a self-diagnostic system that could sense the actual chemical condition of the lubricating oil in intermittently operated machines, and provide an operator or maintenance person with an indication when the oil has reached a certain point of chemical degradation. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a system for detecting the chemical condition of lubricating oil within the oil reservoir of an intermittently operating machine, such as an internal combustion engine, in order to determine the maintenance needs of the lubricant. 
     It is another object of the invention to provide an informational display indication that will notify a user when the lubricating oil is degraded beyond a specified point, to thus allow prompt replacement of the oil. 
     It is another object of the invention to provide a system for detecting the condition of lubricating oil within the oil reservoir of an internal combustion engine by a sampling/analysis sequence which is initiated when the engine is switched off and which sequence continues during engine cool-down. 
     It is yet another object of the invention to provide a system for sensing the composition of vapors in the head space of an oil reservoir where most sensor data acquisition occurs during the period when the engine is not in operation. 
     The above and other objects are realized in a system and method for determining the condition of oil in an oil-utilization mechanism which has an oil reservoir having a head space above the oil, said system comprising: a sensor means for sensing the composition of vapor in the head space and for developing a signal representing said composition; a processor for receiving the signal and for determining if the signal corresponds to predetermined parameters; and apparatus for producing a discernable indication if the processor determines that the signal deviates from the predetermined parameters. 
     In accordance with one aspect of the invention, a system for sensing the composition of vapors within an oil reservoir of an internal combustion engine initiates a sampling/analysis sequence when the engine is switched off, which sequence continues during engine cool-down. 
     In accordance with another aspect of the invention, a sample of oil is removed from the oil reservoir of a continuously running machine and deposited in a holding reservoir. A sampling/analysis sequence of the vapors within a head space of the holding reservoir is initiated when the oil sample is placed in the holding reservoir, and continues as the oil sample cools down. 
     Other objects and features of the present invention will be apparent to those skilled in the art, based on the following description, taken in combination with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of one embodiment of the self-diagnostic system of the present invention installed in an internal combustion engine; 
     FIG. 2 is a graph of an illustrative cool-down temperature curve of engine oil and sensor array of an internal combustion engine beginning at engine shut-down; 
     FIG. 3 is a representation of the three-dimensional time- and temperature-dependent dynamic vapor signature of the oil reservoir vapors; 
     FIG. 4 is a schematic diagram of an artificial neural network for accepting inputs from a plurality of sensors in order to create a dynamic vapor signature; and 
     FIG. 5 is a schematic diagram of an alternative embodiment of the invention configured for use with a continuously running oil-utilizing machine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic diagram of one embodiment of the self-diagnostic system of the present invention. Shown is an engine  10  with an oil reservoir  12 , such as the crankcase of the engine, having a head-space  14  above the free surface  16  of the oil. Alternatively, it will be apparent that instead of an engine, the present invention could be used in a transmission of an internal combustion engine, a gas turbine engine or jet engine, a hydraulic machine, or any other oil-utilizing machine subject to intermittent use and having an oil reservoir. 
     A sensor array  18  is disposed in communication with the head space  14  via a conduit  20  which will allow the head-space vapors to travel to the array for sampling. The vapors are transported through the conduit  20  by means of a micropump  22  which creates suction to draw the vapors to and through the sensor array. The vapors are then exhausted to the outside through a vent  24  after sensing. Alternatively, if required for environmental or other reasons, the vapors may be circulated back into the engine, for example for combustion, through another conduit  26 . 
     The mixture of volatile degradation products in the head-space above the lubricant represents a chemical signature that identifies the composition, i.e., the state of the oil. As noted above, these degradation products of the oil are typically oxidized forms of hydrocarbons including C 6 -C 20  aliphatic carboxylic acids, C 6 -C 14  carboxylic aldehydes, C 6 -C 14  aliphatic esters, and C 6 -C 12  unsaturated aldehydes. The degradation products may also include aromatic acids, aromatic aldehydes, and polycondensed aromatic hydrocarbons. Antioxidants may also be present, which gradually disappear as the oil degrades. Chemical changes taking place in the lubricating oil may be detected by sensing the changes of composition of these volatile degradation products in the gas phase (head-space) above the lubricant. As will be apparent to one knowledgeable in the field, the presence of these degradation products increases as the oil becomes progressively more degraded over time. These volatile combustion products are in a dynamic equilibrium with the components of the oil and indicate the status of the lubricant, i.e. the need for replacement. 
     The sensing array  18  preferably consists of 6 to 10 sensing elements, each preferably sensitive to a different degradation component of the oil. A greater number of sensing elements (i.e. more than 10) could be provided if desired for more complete and accurate sampling of the head-space vapors, but are not necessary for adequate implementation of the present invention. The sensing elements may be electrochemical, optical, mass, thermal, or any combination thereof to form an array. The preferred sensor type is an electrochemical sensor which detects conductivity changes. See J. Janata,  Principles of Chemical Sensors  (New York, Plenum Press, 1989). One example of such a sensor is a semiconducting tin oxide type sensor such as the Figaro TGS series available from Figaro Engineering, Inc., Japan. 
     The detected change of the head-space composition constitutes a typical chemical signature corresponding to the state of the lubricant. Fresh oil also has a characteristic signature which, in the conditioned-maintenance system of the present invention, represents the baseline against which the progressive degradation is measured. 
     The sensor array  18  is connected to a microprocessor  28  which receives signals from the various sensing elements. The processor  28  also receives signals from a temperature probe  30  disposed in the oil reservoir  12  to detect the temperature of the oil, and from another temperature probe  32  disposed adjacent to the sensor array  18  to detect the temperature of the sensor array. The oil reservoir temperature probe  30  is important to the system of the present invention because the rate of change of the composition head-space vapors varies as a function of the temperature of the oil. The sensor array temperature probe  32  is employed because the performance of the sensor array depends in part on its operating temperature, which may vary significantly from the temperature of the oil. 
     The sensing array will absorb heat from the engine and from the head-space vapors, but may be physically separated some distance from the engine itself, and typically will not attain the same temperature as the engine oil, as shown by the curve of FIG.  2 . Consequently, the cooling curve response profile must be corrected for the effects of the temperature changes of the sensing array itself, which should be independently measured. Those skilled in the art will recognize that correcting the response profile can be easily done by normalizing the cooling curve to the difference in temperature between the oil and the sensing array. 
     Additionally, the performance of most sensors is degraded when they must operate under vibration. This is particularly true of mass sensors. Because the invention here described acquires data when the engine is not in operation, it operates in an essentially vibration free environment. It will be apparent that this configuration will enhance both the performance and useful life of the sensors. Moreover, by operating when the engine is not in use, a generous amount of time is made available for data acquisition and data processing. 
     The microprocessor  28  analyzes the signals transmitted to it, and provides output in a user-friendly format such as through an indicator light, CRT, or other visual display  34 , or alternatively, through other indications such as audible signals, to notify the user or maintenance personnel of the condition of the oil. It will be apparent to those skilled in the art that other modes of output may also be advantageously employed to accomplish the same purpose. 
     The system of the present invention uses a novel sampling/analysis sequence, which may be initiated when the engine  10  is shut off or some preprogrammed delay time thereafter, and the oil begins to cool down. Alternatively, the invention can be used with continually running machines, as described in more detail below. A graph of the cool-down temperature curve of the engine oil and sensor array beginning at engine shut-down is provided in FIG.  2 . As the temperature of the oil decreases after engine shut-down, the chemical composition of the head-space vapors changes according to the type and concentration of its volatile components. The most volatile components, such as aliphatic esters and alcohols, stay in the gas phase the longest, while the least volatile components, such as aliphatic acids and aldehydes, disappear. As noted above, the rate of these composition changes is a function of the temperature of the oil. 
     The response from the integrated chemical sensing array  18  is obtained at pre-determined temperature intervals during the cool-down phase, shown as T 0 , T 1 , T 2 , and so forth in FIG. 2, and is evaluated by the on-board microprocessor  28  to determine a signature of the oil vapors. A three-dimensional representation of the time- and temperature-dependent dynamic vapor signature of the oil reservoir vapors is given in FIG.  3 . In this figure the several discrete peaks represent the time and temperature dependent signature of the various constituent degradation products present in the oil vapor. The three-dimensional graph thus represents a landscape or signature of either “good” or “bad” oil. The absolute values, positions, or number of peaks in this landscape do not have any particular meaning except as an indication of the state of the oil. The mode of analysis is similar to the decision made by an experienced wine taster who does not know the composition of the wine, but can nevertheless determine the type, quality, and even the vintage of the product. This approach is commonly known as artificial intelligence or in the case of gas sensing, “electronic nose.” The strategy for recognizing the patterns of like complex mixtures is called pattern recognition. 
     There are several pattern recognition packages available to perform this task. One such technique is called Artificial Neural Networks or ANN. See D. E. Rumelhart, G. E. Hinton, R. J. Williams, “Learning Representations by Back Propagating Erros”, 323 Nature 533-536 (1986). A scheme for ANN as part of the present invention is shown in FIG.  4 . Raw inputs  50  from an array  52  consisting of a plurality of sensors (four sensors shown for simplicity) are fed into the first input layer of amplifiers  54 . From there, the outputs are fed to a plurality of elements of hidden layer amplifiers  56  which multiply the inputs by a predetermined coefficient during the “learning” phase of the ANN. The “learning” is performed automatically by presenting the ANN with the mixture of known composition and adjusting the outputs from the output layer  56  to the desired values. The time- and temperature-dependent dynamic vapor signature of the oil vapors is determined by the configuration of the entire group of output values  58  at a plurality of sampling times during the sampling cycle. 
     This “learning” of the ANN is performed for the “good” oil and the values of the amplification factors are permanently stored, such as in computer memory, as the signature of the “good” oil. The ANNs can be implemented either in the software or in the hardware form. As noted, the absolute concentrations of individual degradation products in the head space or their algorithmic relationship to the composition of the oil is not necessary. 
     Another pattern recognition algorithm that may be advantageously employed in the present invention is called Visual Empirical Region of Influence (VERI), developed at Sandia National Laboratories. See G. C. Osbourn, J. W. 
     Bartholomew, A. J. Ricco, and G. C. Frye, “Visual-Empirical Region-of-Influence Pattern Recognition Applied to Chemical Microsensor Array Selection and Chemical Analysis”, 31  Account of Chemical Research  297-307 (1998). VERI computes distances between data points in the n-dimensional space (where n is the number of sensors in the sensing array). 
     The training or “learning” of this algorithm is similar to ANN, again based on the response of the array to the known standard. In both ANN and VERI pattern recognition techniques the deviation of the actual signature (i.e. progressively deteriorating oil) is compared with the baseline or standard signature (i.e. the “good” oil). The microprocessor “decision” whether to advise changing the oil or not is based on the chosen magnitude of acceptable deviation between “good” oil and “bad” oil. 
     The preferred diagnostic schedule would be as follows. The engine is operated for a minimum predetermined time and reaches a standard operating temperature. The corresponding temperature of the oil is T o  (FIG.  2 ). The diagnostic sequence commences immediately after the engine ceases its operation (or when the oil sample is removed from the oil reservoir and placed in the holding reservoir). The response of the head-space changes is recorded at different points, T 0 , T 1 , T 2 , etc., on the cooling curve (FIG. 2) This time-and-temperature-dependent “dynamic” information for each sensor becomes a part of the diagnostic test (FIG.  3 ). 
     After the oil cools down completely, the baseline value of the “signature” T b  is obtained. Because of its design, the diagnostic system of the present invention is self-calibrating since the composition of the head-space under a cooled-down condition is expected to be constant or nearly constant. Both the “cold” and the “hot” signatures are compared to the “cold” and the “hot” signatures corresponding to the fresh oil, and the deviation of these signatures provides the desired information about the required lubricant change. 
     This information is made available in a user-friendly form prior to initiating the next duty cycle. The typical scenario for a motor vehicle, according to this scheme, can be described as follows: The vehicle is operated for a minimum required time and then parked. The diagnostic sequence starts immediately (or, alternatively, after a selected delay). The data is obtained and analyzed during the rest period, and after complete cool down the system calibrates itself. The microprocessor retains in memory the calibration signature, and the cycle is repeated again. The microprocessor compares the calibration signatures of the n&#39;th and the n-1 run, and the results are made available to the operator prior to the next duty cycle with appropriate recommendations for action. 
     Monitoring of the chemical status of the oil is the great advantage of the present invention, and is the fundamental idea behind condition-based maintenance. Instead of following a necessarily approximate mileage or hours of operation schedule for oil changes, maintenance can be scheduled based on the directly identified needs given by the chemical state of the lubricant. Condition-based maintenance thus saves both labor and material costs in engine maintenance, as well as decreases the volume of pollutants such as waste oil discarded into the environment. The main distinguishing feature of the present invention is that the information acquisition is done dynamically by a multi-sensing array while the engine is not operating. 
     Another significant advantage of the present invention is the baseline time determination feature. The data collection of this invention relies on the time dependent changes of the head space composition (profile) collected after each duty cycle. Turning the engine off (or withdrawing the oil sample) provides a precise determination of t=0 from which the data acquisition during the cooling period begins. Thus, the time dependence of the profiles of the composition of the head space becomes the part of the signature of the “good” or “degraded” lubricant. The “zero time” aspect of this information acquisition prevents one notorious problem of chemical sensors/arrays: baseline drift. That is, each T n =0 for the n-th profile establishes a new baseline. That type of information and such benefits would not be available for monitoring of the head space above the lubricants in continuously operating systems, e.g. in transformer oil because the profile at t=0 could not be accurately established. 
     The inventors have found that other classes of gaseous compounds are also present in the head space above used oil in addition to those mentioned above. For example, aromatic acids such as benzoic acid, aromatic aldehydes such as benzaldehyde, and polycondensed aromatic hydrocarbons such as napthalene and biphenyl may also be present in varying concentrations the gas phase above used oil. The inventors have configured sensors to detect these classes of compounds, and have included the concentration of these constituents in the time and temperature based vapor signature which signals the condition of the oil. 
     The inventors have also discovered that the disappearance of various antioxidants from the head space vapor is a further indication of degraded oil. Producers of lubricating oils routinely add antioxidants to slow the rate of oxidation of the hydrocarbons, thus slowing the rate of breakdown of these compounds. When these compounds are present in the oil, they will also have a representative vapor pressure which will cause them to be present in gaseous form in the head space of the oil reservoir. As the oil degrades, however, these antioxidants will gradually disappear. When these antioxidants disappear, this signals that the oil has begun to oxidize, and should be replaced. The inventors have found that by detecting the presence and disappearance of antioxidants such as diphenylamine, and 2,6-dibutylphenol the condition of the oil can be further determined. 
     Sensors to detect many of the chemical compounds mentioned above are commercially available. Others are not commercially available, and must be custom made for a particular application. One type of sensor which is suitable for the present invention is an array of chemically sensitive field-effect transistors (CHEMFET) employing specially designed selective layers based on conducting polymers. These layers are selectively sensitive for degradation products or antioxidants discussed in the present invention. Sensors of this type are commercially available such as from Nordic Sensor Technologies, Linkoping, Sweden. 
     Other suitable sensors include chemiresistors employing conducting polymer layers selected for particular degradation products or antioxidants discussed above. A commercial chemiresistor array can be purchased e.g. from Cyrano Sciences, Pasadena or City Technology, Ltd., Portsmouth, England. Another example is an array of mass sensors (thickness shear monitors (TSM) or surface acoustic wave devices) employing non conducting polymer selective layers. Commercial TSM arrays can be obtained e.g. from MOTech, GmbH, Tubingen, Germany. 
     Another example is an array of optical fiber sensors or optical waveguide sensors employing optically sensitive, selective layers. A sensing array of this type can be obtained from e.g. Illumina, Inc., Massachussets. These are only illustrations of types of chemical sensors that could be used for the present application. The key element of these sensors are the selective layers that have to be developed individually to provide selective response to the individual gases that constitute the “signature” of the used and of the new oil. Such layers are then assembled into an array. The operating principles of the individual sensors are described in J. Janata, “Principles of Chemical Sensors”, Plenum, 1988. 
     An alternative embodiment of the present invention could be configured for use with continuously running oil utilizing machines. For example, marine turbine engines, industrial motors, generators, and other oil-utilizing machines experiencing intermittent loads may run for long periods of time between shutdown. In such machines, it becomes impractical or uneconomical to wait for shutdown in order to sense the condition of the oil and create a time and temperature based vapor signature. Accordingly, FIG. 5 depicts an alternative embodiment of the present invention configured for sensing the condition of oil in a continuously running oil utilizing machine  110 . As with the other embodiments described above, the machine  110  has an oil reservoir  112  having a head-space  114  above the free surface  116  of the oil. 
     However, in this embodiment, rather than connecting the sensor array  118  directly to the head-space  114 , a hot sample of liquid oil is pumped via pump  140  through conduit  142  to a holding reservoir  144 . It will be apparent that rather than using pump  140 , the oil sample could alternatively be obtained by tapping a pressurized oil line associated with the machine  110 , thus allowing the oil pump of the machine to do the work of sending a sample to the holding reservoir. Other means of placing an oil sample in the holding reservoir could also be utilized. For example, a user could manually open a valve associated with the oil reservoir, and allow oil to flow into a container, then transfer the hot oil from the container to the holding reservoir. Alternatively, the holding reservoir  144  could be located below the elevation of the oil reservoir  112 , so that when an appropriate valve is opened the oil will flow into the holding reservoir by means of gravity. Any system which will allow a sample of oil from the oil reservoir  112  to be transported to the holding reservoir  144  will be suitable. 
     The oil sample pumped into the holding reservoir will give off vapors into the head space  146  of the holding reservoir, and these vapors are allowed to travel via gas conduit  120  to the sensor array  118  for sampling. As with the other embodiments discussed above, the vapors are transported through conduit  120  by means of a micropump  122  which draws the vapors to and through the sensor array. The vapors may then be exhausted to the atmosphere through vent  124  after sensing, or may be circulated back into the machine  110  through conduit  126 . 
     Temperature probes  130  and  132  detect the temperature of the oil sample and sensor array  118 , respectively, and this information, along with the sensor array data, are transmitted to a microprocessor  128 , which processes the signals in the manner discussed above, to create a time and temperature based vapor signature. In this embodiment, the sampling/analysis sequence is initiated when the oil sample is pumped into the holding reservoir  144 , or some preprogrammed delay time thereafter, rather than when an engine or other machine is shut off. Consequently, the machine  110  may continue running without interruption. As described above, the integrated chemical sensing array  118  detects the composition of the vapors in the head space  146  at pre-determined temperature intervals as the oil cools down to approximate thermal equilibrium with the outside environment. 
     It will be apparent that the processor results could be presented in some humanly discernable form through a display  134 . Alternatively, the processor results could be directly communicated to other computer devices or machines in order to directly affect the operation of the machine  110 . For example, the processor could be interconnected with the electrical control system of the machine, so as to cause the machine to run differently or not at all depending upon the condition of the lubricating oil. 
     Once the oil in the holding reservoir  144  has completely cooled and the sampling process is complete, the oil may be returned to the oil reservoir  112  by means of second pump  148  and-conduit  150 , or may be drained from holding reservoir  144  and discarded. Valves  152  and  154  may be provided in the oil conduits  142  and  150  to selectively allow the oil to flow as desired, and checkvalves  156  and  158  may also be provided to prevent backflow. Additionally, rather than having a second pump  148 , pump  140  could be configured through selective valving and arrangement of oil conduits to perform both the operations of pumping the hot oil sample to the holding reservoir  144 , and returning the cooled sample to the oil reservoir  112 . 
     This self-diagnostic system could be implemented in a wide variety of applications. For example, it would be ideal for the military for engines that are operated under widely varying conditions and loads where time dependent maintenance schedules are difficult to estimate. It could also be used in the civilian sector such as for construction and heavy earth moving machinery, in private automobiles, commercial and private aircraft, ships, and so forth where maintenance schedules are more easily predicted, but may still be unrealistic. Such applications could include internal combustion engines, such as gas or diesel engines, gas turbine or jet engines, and industrial equipment and machines of various kinds. Additionally, hydraulic machines which utilize hydraulically actuated moving parts also use oil which degrades over time. There are a wide variety of such machines, including excavators, loaders, scrapers, dump trucks, power shovels, forklifts, etc. While standard hydraulic fluid typically degrades more slowly than engine lubricating oil, these machines also can benefit from the present invention. Any oil-utilizing machine which operates under intermittent loads such that it is difficult to predict the actual life-expectancy of the oil based on time of use, mileage, etc., is a good application for this system. In all cases, the use of such a system would result in decreased maintenance labor and material costs, decreased environmental waste, and increased useful lifetime of the machines. 
     It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements.