Patent Publication Number: US-2004047391-A1

Title: Apparatus and method for viscosity measurement

Description:
BACKGROUND OF THE INVENTION  
       [0001] This invention relates generally to measuring viscosity and more particularly to a method and apparatus for measuring the change in viscosity of a fluid as the condition of the fluid deteriorates.  
       [0002] Hydraulic oil such as lubricating oil for an internal combustion engine inevitably experiences changes in its viscosity over time as a function of oil grade, temperature, state of deterioration and other operational parameters. Oil viscosity is an important property because it defines the oil film thickness between moving parts of an engine. It also affects cold crank capability, fuel consumption and for some engines it influences the ability to control emissions such as in a diesel injection system with a hydraulic booster. Oil viscosity may also be used to determine the end of the oil&#39;s useful life. For example, a predetermined threshold value of oil viscosity may be used alone or in conjunction with other oil properties such as oil acidity, particle count, content of certain additives and level of contamination to signify that a volume of oil has reached the end of its useful life and needs to be replaced or reconditioned.  
       [0003] The necessity of changing oil in an internal combustion system such as an automobile is typically determined based on recommendations made by the manufacturer and found in the vehicle&#39;s owner&#39;s manual. Such recommendations are based on assumptions that may or may not apply to a particular user&#39;s specific environmental and/or driving conditions. Changing oil based on the manufacturer&#39;s recommendations may be satisfactory in many circumstances. However, if an inferior grade of oil is used or an engine is operated in a harsh environment the proper interval for oil change may vary as a function of predetermined oil condition parameters, one of which may be viscosity. Consequently, the ability to measure oil viscosity quickly and accurately may be useful to avoid damage to an engine.  
       [0004] One known method for determining viscosity employs an arrangement that purportedly measures the viscosity of a fluid by determining the time required for a standard element to travel a predetermined distance through the fluid. This arrangement is not capable of in-situ measurements of oil viscosity, which may be desirable in many applications such as in the automobile industry. Other devices and methods are known for measuring viscosity that require samples of the liquid in question to be taken to a laboratory of other facility for analysis. These techniques are not suitable for in-situ measurements.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005] One exemplary embodiment of the present invention provides an in-situ method and apparatus for measuring the change in viscosity of a lubricant as the quality of the lubricant deteriorates during operational use. One aspect of the present invention allows for the correlation of the heat convection properties of the lubricant to the lubricant&#39;s viscosity. A heating means may be provided for locally increasing the lubricant&#39;s temperature. At least a portion of the heated lubricant may then rise within the bulk lubricant volume due to the heated portion&#39;s reduced density. An operational rise time may then be determined, which may be determined after a vehicle is shut down, for example, to determine the necessity of changing or treating the bulk lubricant. The operational rise time may be the difference between the actuation of a heat pulse from the heating means to heat a portion of the bulk lubricant and the arrival of the heated portion at a predetermined distance from the heating means. The operational rise time may then be used to determine the bulk fluid&#39;s viscosity.  
       [0006] An alternate embodiment allows for the operational rise time to be the amount of time it takes the heated portion to rise from a position proximate the point at which it is heated to a position proximate a second point that is a known distance from the first point. Yet another alternate embodiment allows for determining the heated portion&#39;s average velocity, which may be determined as a function of the temperature difference between the heated lubricant portion and the rest of the bulk lubricant volume. The average velocity may also be a function of shear forces within the lubricant, which are determined by the lubricant&#39;s viscosity.  
       [0007] One aspect of the present invention allows for creating a set of look up tables containing baseline rise times at a known temperature for a set of bulk fluids having a known viscosity. The operational rise time may then be compared to the appropriate baseline rise time contained in the look up table to determine the viscosity change of the bulk lubricant. The baseline rise time data may be interpolated to determine qualitative and/or quantitative information regarding the viscosity of the bulk lubricant in response to determining the operational rise time. This information may then be used to determine whether the bulk lubricant needs to be changed or treated.  
       [0008] One embodiment of the present invention allows for a temperature sensor to take a first temperature at a predetermined height to establish a baseline temperature of the bulk lubricant at that height. The heating means may heat a portion of the bulk lubricant at a predetermined point below the predetermined height. The amount of time it takes the heated portion to rise from the heating means to the predetermined height may be measured by determining when the temperature change occurs at the predetermined height. A change, if any, in the viscosity of the fluid may then be determined.  
       [0009] Another aspect of an exemplary embodiment of the present invention allows for at least one temperature sensor to be used in a quantity of bulk oil for measuring a temperature as a quantity of heated lubricant passes a known point. In an alternate embodiment two temperature sensors may be used to measure temperature change between a first point and a second point in the bulk oil as the heated oil passes between those points. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010]FIG. 1 illustrates a cross section of a container for holding a fluid with an exemplary embodiment of the present invention contained therein;  
     [0011]FIG. 2 illustrates a cross section of a container for holding a fluid with another exemplary embodiment of the present invention contained therein;  
     [0012]FIG. 3 illustrates a cross section of a container for holding a fluid with another exemplary embodiment of the present invention contained therein; and  
     [0013]FIG. 4 is a flow diagram of an exemplary method in accordance with one aspect of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0014]FIG. 1 illustrates a cross section of a container  10  for holding a quantity of bulk fluid  12  such as petroleum-based oil used as a lubricant for lubricating and cooling moving components of the internal combustion engine of an automobile, for example. A heating means  14  may be provided to locally heat a portion  16  of the bulk fluid  12 . The heating means  14  may be a conventional heat source such as a smart heating source, for example, adapted to control voltage and current. In alternate embodiments the heating means  14  may be other conventional devices such as radiative, resistive, and inductive heaters, for example. A temperature sensor  18  may be provided to measure a change in temperature at a predetermined point above the heating means  14 . The temperature sensor  18  may be a conventional device such as a resistive thermal device (“RTD”), thermocouple, thermometer or other devices known in the art. The heated portion  16  of bulk fluid  12  will rise after being heated due to its lower density relative to the bulk fluid  12 . One exemplary embodiment of the present invention allows for correlating the amount of time it takes the heated portion  16  to travel a known distance through the bulk fluid  12  with viscosity in order to measure a change in viscosity of the bulk fluid  12 . The heated portion  16  may cool as it rises in the bulk fluid  12  due to the thermal conductivity of the bulk fluid  12  and the heated portion  16 . However, the thermal conductivity of petroleum-based lubricants such as those used in automobiles, for example, are substantially equal and whatever effect thermal conductivity has on the heated portion  16  is substantially the same among the lubricants. Other embodiments of the present invention may take into account differences in thermal conductivity among bulk fluids to the extent the differences impact the determination of viscosity changes in those fluids.  
     [0015] The temperature sensor  18  may be used to detect a change in temperature of the bulk fluid  12  at a predetermined point or height B above the heating means  14 . After heating, the velocity of the portion of heated fluid  16  when moving distance d between points A and B is a function of at least: a) the temperature difference between the bulk fluid  12  and the heated portion  16 , and b) the viscosity of the bulk fluid  12 . In one exemplary embodiment the distance d may be between about one (1) to two (2) centimeters and the temperature difference between the bulk fluid  12  and the heated portion  16  may be about 5 degrees Celsius. Distance d and the temperature difference between the heated portion  16  and the bulk fluid  12  may vary in alternate embodiments of the present invention depending on specific design, performance and other parameters. For instance, the temperature difference between the heated portion  16  and the bulk fluid  12  may be a function of the duration of a heat pulse generated by the heating means  14 . The longer the heat pulse the greater the temperature differential. It is desirable to provide a heat pulse that results in a sufficiently stable or defined heated portion  16 . This allows for the heated portion  16  to travel through the predetermined distance without diffusing too much into the bulk liquid  12  or otherwise having its physical properties degrade before it reaches the temperature sensor  18 , for example. Similarly, if the heated portion  16  is not sufficiently heated it may not travel to the temperature sensor  18  with sufficient characteristics for the sensor  18  to detect a temperature change. It has been determined by the assignee of the present invention through empirical testing that providing a heat pulse generally between about 0.5 and 1.0 seconds allows for the heated portion  16  to travel an appropriate distance to have its operational rise time determined. Alternate embodiments may provide for a heat pulse of greater or lesser values depending at design parameters of the viscosity sensor. For example, in one exemplary embodiment the heat pulse may be as short as about 0.10 seconds. Thus, it will be appreciated that the present invention is not limited to any specific time duration for heating portion  16 .  
     [0016] One aspect of the present invention allows for determining the operational rise time of the heated portion  16 . In one exemplary embodiment the operational rise time may be defined as the time difference between the time a heat pulse from heating means  14  is actuated and the time the heated portion  16  “arrives”, or is initially detected, at a point a known distance away such as point B proximate the temperature sensor  18 . The temperature sensor  18  may detect a localized change in temperature of the bulk fluid  12  that is indicative of the “arrival” of the heated portion  16 . As the heated portion  16  rises toward height B the temperature sensor  18  will detect a temperature change in the bulk liquid  12  proximate the temperature sensor  18 . This is due to the heated portion  16  rising sufficiently close to the temperature sensor  18  so that the sensor may measure a local change in temperature of the bulk fluid  12 . In an alternate embodiment, the “arrival” of the heated portion  16  may be detected by a laser diode that detects a change in the index of refraction of the heated portion  16  as it passes near the sensing area. The temperature sensor  18  may be configured to send a data signal to a processor  22  that the heated portion  16  has been detected. The processor  22  may then calculate the operational rise time and/or the average velocity of the heated portion  16 . The operational rise time may then be compared to a baseline rise time for that bulk fluid  12  via a lookup table stored in a database accessible by the processor  22 , for example. The baseline rise time may be determined for the bulk fluid  12  at a selected temperature when the bulk fluid&#39;s  12  viscosity is known such as before the bulk fluid  12  is subjected to operating conditions in container  10 . In alternate embodiments the operational rise time of the heated portion  16  may be calculated over a different distance d, such as the time it takes the heated portion  16  to move between any two known points, provided that the baseline rise time is calculated using the same points. Thus, measuring changes in temperature over a distance d should not be construed as a limitation of the present invention. The assignee of the present invention has determined through empirical experimentation that the difference between the baseline and operating rise times is indicative of a change in viscosity of the bulk fluid  12 . The viscosity of the surrounding bulk liquid  12  will affect the rise rate of the heated portion  16 . The greater the viscosity of the surrounding bulk fluid  12  the more slowly the heated portion  16  will rise.  
     [0017] A control circuit  20  and the processor  22  may be provided for data analysis and as means for controlling the temperature sensor  18 , heat source  14  and/or a display device  24 . The control circuit  20  and processor  22  may be separate components or they may be combined into one unit as will be recognized by those skilled in the art. Processor  22  may be configured with appropriate software to calculate the difference between the baseline rise time and the operational rise time for a selected bulk fluid  12 . The difference may then be used to determine whether that bulk fluid  12  has experienced a change in its viscosity. The processor  22  may be programmed to express a change in viscosity in qualitative and/or quantitative terms. An electronic data signal indicative of any change in the viscosity of the bulk liquid  12  may be generated by the processor  22  and sent to a display device  24 , for example, by the control circuit  20 . One aspect of the present invention allows for selecting a set of criteria for determining whether the processor  22  will send a signal to the display device  24 , for example, and what information that signal will contain. For example, the set of criteria may include a variety of variables such as a predetermined percentage change in the viscosity of the bulk fluid  12 . If the percentage change in the viscosity of the bulk fluid  12  from the baseline viscosity or previous viscosity reading is equal to or greater than twenty percent (20%) then the data signal may cause the display device  24  to indicate that it&#39;s time to change the bulk fluid  12 . Alternate embodiments may include other variables such as recommendations from an automobile manufacturer for changing the automobile&#39;s oil based on environmental conditions, oil conditions, viscosity changes, etc. In one exemplary embodiment of the present invention the display device  24  may be part of the control panel of an automobile and may indicate to the driver, based on predetermined conditions, that the motor oil, for example, needs to be changed soon or that it needs to be changed as immediately as possible. It will be recognized by those skilled in the art that the display device  24  may be a variety of other types of devices that may be stand alone devices or integrated with other devices.  
     [0018]FIG. 2 shows another exemplary embodiment of an apparatus in accordance with another aspect of the present invention. A container  10  similar to the one shown in FIG. 1 may hold a quantity of bulk liquid  12  such as the motor oil of an automobile, for example. In one exemplary embodiment the container  10  may be the oil pan of an automobile but it will be recognized by those skilled in the art that container  10  may comprise a wide range of other types of containers used for other purposes. A heating means may be provided, such as heat source  30 , situated near the bottom of the container  10  to heat a portion of the bulk liquid  12 . Heat source  30  may be any conventional heat source such as a glow plug, or other resistive heaters, as well as inductive, conductive, or radiative heaters connected to a power supply, for example. The heated portion  32  of bulk liquid  12  will rise within the bulk liquid  12  due to its lower density relative to the bulk liquid  12 . A first temperature sensor  34  and a second temperature sensor  36  may be provided in spaced relation within the bulk liquid  12 . Sensors  34  and  36  may be conventional heat sensors such as a resistive thermal device, thermocouple, thermometer or other such device. In one exemplary embodiment each of the sensors  34  and  36  may be a resistive thermal device (“RTD”) configured to generate an output signal in response to changes in resistance. For example, sensor  34  may generate a first output signal  40  and the sensor  36  may generate a second output signal  42 . The output signals  40  and  42  may change in response to changes in the resistance of each sensor  34  and  36  as the heated portion  32  moves past each sensor&#39;s respective position within the bulk liquid  12 . In this respect, each sensor  34  and  36  exhibits increasing resistance as the temperature of the bulk liquid  12  near them increases. A signal processor  44  may be provided to amplify the first and second output signals  40  and  42  and calculate an output signal  46  by subtracting the second output signal  42  from the first output signal  40 . As shown in FIG. 2, the heated portion  32  is shown in different positions as it rises within the bulk liquid  12 . The heated portion  32  may rise so that it passes the first sensor  34  and the second sensor  36 . As the heated portion  32  first approaches and then passes first sensor  34 , the first output signal  40  may change in response to the higher temperature of the heated portion  32 . Similarly, as the heated portion  32  approaches and passes the second sensor  36 , the second output signal  42  may change in response to the higher temperature of the heated portion  32 . The output  46  may be used by the processor  44  to calculate the operational rise time of the heated portion  32 . The operational rise time may be calculated by the processor  22  and be defined as the time it takes the heated portion  32  to travel between the sensors  34  and  36 . As suggested above, other embodiments may calculate the operating rise time using different reference points provided that the operating rise time may be compared to a corresponding lookup table to determine a change in viscosity of the bulk fluid  12 .  
     [0019] In an alternate embodiment, the velocity, average velocity and/or acceleration of the heated portion  32  may be determined in the region of the temperature sensors  34  and  36 , for example. Empirical testing conducted by the assignee of the present invention has demonstrated that the velocity, average velocity and operating rise time of the heated portion  32  is directly or monotonically related to the viscosity of the bulk liquid  12 . This is true for any heated portion  16 ,  32  and  53  illustrated in the Figures. That is, the movement of a heated portion through the bulk fluid  12  is a function of the bulk fluid&#39;s  12  viscosity. The velocity or average velocity increase in response to a decrease in the viscosity of bulk fluid  12 . Similarly, the operating rise time decreases in response to the viscosity of the bulk fluid  12  decreasing. Measuring the velocity, average velocity and/or operating rise time of a heated portion  16 ,  32  or  53  allows for a qualitative and/or quantitative measurement of the bulk liquid&#39;s  12  viscosity to be determined by comparing those measurements to a corresponding lookup table or tables and making appropriate interpolations.  
     [0020] Another exemplary embodiment of the present invention is shown in FIG. 3, which illustrates a substantially cylindrical tube  50  submersed within the bulk liquid  12  that may act as a housing or means for shielding the heated portion from crosscurrents. In alternate embodiments, the tube  50  may be other shapes such as rectangular, oval, square, polygonal, etc. provided that the heated portion of the bulk fluid  12  is substantially shielded from crosscurrents in the fluid  12 . Tube  50  may be submersed so that it contains a portion of the bulk liquid  12  and may be made of conventional materials such as high temperature metal, ceramic, or plastic, for example. The bulk liquid  12  may be contained within the container  10 , which may be the oil pan of an automobile, for example. In one exemplary embodiment the tube  50  may be attached to a base (not shown) of a sensing apparatus, having a variety of sensing means, with the base affixed to the exterior of an automobile&#39;s oil pan, for example. In this respect, the tube  50  may extend upright into the bulk liquid  12  contained within the oil pan. In alternate embodiments, the tube  50  may be affixed directly within container  10 . Heating means  52 , such as the heat source  14  of FIG. 1 and the heat source  30  of FIG. 2, may be provided as means to heat a portion  53  of the bulk liquid  12 . Temperature sensing means  54 , such as the temperature sensor  18  of FIG. 1 and the sensors  34  and  36  of FIG. 2, may be provided as means for detecting a change in temperature of the bulk liquid  12  proximate the sensing means  54 . A processor and control circuit  56  may be provided to control the temperature sensing means  54  and the heating means  52  and to calculate the velocity, average velocity and/or operational rise time of the heated portion  52  as it travels distance d shown in FIG. 3. In one exemplary embodiment distance d may be between about one (1) and ten (10) centimeters but may be other distances as a function of design parameters. Those skilled in the art will recognize that distance d may vary with at least the size of container  10  and tube  50  as well as the properties, including viscosity, of the bulk liquid  12 . One advantage of providing tube  50  is that it may reduce or eliminate crosscurrents in the bulk liquid  12 . This may be desirable because crosscurrents in the bulk liquid  12  may disrupt the flow or upward motion of the heated portion  32  causing less accurate calculations of the bulk liquid&#39;s  12  viscosity. Tube  50  may range in its size as a function of design parameters. Capillary forces should be taken into account for tube&#39;s  50  having small diameters. That is, any resistance to the heated portion&#39;s  53  ability to rise within the tube  50  should be derived from the bulk fluid  12  and not due to the geometry of tube  50 . In one exemplary embodiment tube  50  may have a length of approximately one (1) centimeter but other lengths will be recognized by those skilled in the art. It has been determined by the assignee of the present invention that as the path length of tube  50  decreases, the energizing time for a heat pulse generated by heating means  52  should be reduced, with a correspondingly smaller temperature rise in the heated portion  53 . This is to prevent the size of heated portion  53 , for example, from becoming too large relative to the distance portion  53  needs to travel.  
     [0021]FIG. 4 is a flow chart of an exemplary embodiment of a method for measuring viscosity in accordance with one aspect of the present invention. Step  60  allows for establishing or determining a set of baseline parameters associated with a fluid such as the lubricant or oil used in an internal combustion engine of an automobile, for example. Baseline parameters may include the fluid&#39;s viscosity, additives content, thermal conductivity, SAE rating and other parameters associated with the fluid. One aspect of the present invention allows for establishing a baseline rise time at a predetermined temperature for a lubricant or a range of lubricants. Determining baseline parameters allows for changes in the parameters to be determined based on use of the bulk fluid  12 , for example. Certain changes may indicate that the bulk fluid  12  needs to be replenished or replaced due to the associated parameter deviating too much from their its respective baseline. For example, oil used in an automobile may need to be replaced if the oil&#39;s viscosity becomes too low compared to its respective baseline viscosity and/or if the oil experiences a step change or large decrease in its viscosity from one viscosity measurement to the next.  
     [0022] Step  62  allows for the temperature of the bulk fluid  12  to stabilize prior to determining whether there has been a change in its viscosity. This is to ensure that movement of a heated portion is essentially caused by its being heated by a heating means such as  14  or  34 . One exemplary embodiment allows for the bulk fluid&#39;s  12  temperature to stabilize by waiting a predetermined period of time after an automobile&#39;s engine is shutdown, for example, before heating a portion of the bulk liquid in step  68 . This allows the temperature of the bulk fluid  12  to achieve equilibrium with the ambient temperature. Step  64  allows for the agitation of bulk fluid  12  to stabilize to allow a heated portion of the bulk fluid  12  to rise within the bulk fluid  12  in a non-volatile fluid environment. For example, during the operation of an automobile, motor oil is distributed to moving parts and collects in an oil pan for re-circulation. When the engine is shutdown, the oil collects in the oil pan and stabilizes so that it is not agitating. Step  64 , in one exemplary embodiment, allows for waiting a predetermined period of time after an automobile&#39;s engine is shutdown prior to heating a portion of the bulk fluid  12  to determine a change in its viscosity.  
     [0023] Another aspect of the method illustrated in FIG. 4 allows for the temperature of the bulk fluid  12  to be determined in step  66 . This allows for determining changes in the bulk fluid&#39;s  12  viscosity at more than one temperature. Thus, one could make, if desired, another determination of viscosity after the bulk fluid&#39;s  12  temperature and agitation have stabilized. Accordingly, one aspect of the present invention allows for determining changes in viscosity, for example, at two (2) discrete bulk fluid  12  temperatures after engine shutdown of an automobile. A first measurement may be taken when the bulk fluid&#39;s  12  temperature is approximately 100 degrees Celsius and a second measurement at approximately 40 degrees Celsius, for example. Because viscosity is temperature dependent, this allows for developing a viscosity profile of the bulk fluid  12  at different temperatures that may be used to determine whether the oil in an automobile, for example, needs to be changed. Alternate embodiments may measure viscosity at more than two temperatures. To determine whether there has been a change in the viscosity of the bulk fluid  12 , step  68  allows for heating a portion of the bulk fluid  12  so that the heated portion will rise within the bulk fluid  12 . Step  70  allows for determining the operational rise time of the heated portion as described above. The operational rise time of the heated portion may be used to determine whether there has been a change in the viscosity of the bulk fluid  12  in step  72 . Alternate embodiments may use the velocity and/or average velocity of the heated portion to determine a change in viscosity of the bulk fluid  12 . Step  74  allows for an output signal to be generated, such as by processor  22  (FIG.1), indicative of a change in the viscosity of bulk fluid  12 . The output signal may be sent to a display device such as one found in the control panel of an automobile, for example. The output signal may be based on a set of criteria, such as the bulk fluid  12  experiencing a twenty percent (20%) change in viscosity for example, that, if met, will cause the display device to display a specific message. The message may be that the bulk fluid  12  needs to be changed as soon as possible or that it needs to be changed soon, for example.  
     [0024] While the exemplary embodiments of the present invention have been shown and described by way of example only, numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.