Abstract:
A method for detecting fuel leaking into an oil pan containing oil which is used to lubricate an internal combustion engine utilizes a plurality of sensors. The method includes the step of measuring a plurality of parameters of the oil using each of the plurality of sensors to create measured values. A fuel leakage value is calculated incorporating each of the measured values. The method then determines when the fuel leakage value exceeds a predetermined value.

Description:
BACKGROUND ART 
     1. Field of the Invention 
     The invention relates to a method for measuring the characteristics of oil in an internal combustion engine. More specifically, the invention relates to measuring the characteristics of oil of the internal combustion engine to determine when the oil condition has degraded due to the presence of fuel. 
     2. Description of the Related Art 
     More and more attention is being focused on fuel economy with regard to internal combustion engines of motor vehicles. Internal combustion engines that run on diesel fuel have higher fuel economy than those that run on regular gasoline. Motor vehicles operated using diesel fuel have their disadvantages. One disadvantage is the perception that internal combustion engines operating on diesel fuel produce more air and noise pollution. Currently, technological advances have been made to reduce both types of pollution. 
     Another problem with diesel fuel operated internal combustion engines is fuel leakage. Diesel fuel tends to leak into the oil of an internal combustion engine. The diesel fuel that is added to the oil decreases the viscosity of the oil, regardless of the brand. As the viscosity of the oil drops, as is shown in  FIG. 3 , the oil can no longer form a continuous lubricating film on the components of the internal combustion engine, even under normal operating conditions. The absence of a lubricating film on those components will increase the friction therebetween considerably to the point where it could cause severe or catastrophic wear damage. Fuel leakage into oil also adds to the air pollutants that are emitted by the internal combustion engine. 
     An attempt to detect fuel leakage into the oil reserve may be attempted by measuring the level of oil in an oil pan. This method has serious limitations. First, by only measuring the level of oil in the oil pan, it cannot be distinguished as to whether diesel fuel is entering the oil or whether coolant is entering the oil. Second, simple oil level detection alone will be triggered when oil is added to the internal combustion engine. 
     SUMMARY OF THE INVENTION 
     A method for detecting fuel leaking into an oil pan containing oil which is used to lubricate an internal combustion engine utilizes a plurality of sensors. The method includes the step of measuring a plurality of parameters of the oil using each of the plurality of sensors to create measured values. A fuel leakage value is calculated incorporating each of the measured values. The method then determines when the fuel leakage value exceeds a predetermined value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic side view, partially cutaway, of a motor vehicle powered by an internal combustion engine; 
         FIG. 2  is a perspective view of a sensing assembly incorporating a plurality of sensors; 
         FIG. 3  is a graph of normalized oil viscosity as a function of diesel fuel concentrated; 
         FIG. 4  is a graph showing electrical resistance of oil as a function of temperature; 
         FIG. 5  is a logic chart of one embodiment of the invention; 
         FIG. 6  is a logic chart of an alternative embodiment of the invention; and 
         FIG. 7  is a logic chart of a method used to detect massive fuel leaks into oil. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a motor vehicle  10  is shown schematically and partially cutaway. The cutaway portion of the motor vehicle  10  shows that it is powered by an internal combustion engine  12 . The internal combustion engine  12  is powered by diesel fuel and lubricated by oil, graphically represented by oil level  14 . A reserve of oil is stored in an oil pan  16  that is typically disposed below the internal combustion engine  12 . An oil sensor  18  is shown in phantom within the oil pan  16 . Outputs from the oil sensor  18  are received by a control unit  20  which stores values for sensed parameters in a memory  22  electronically connected to the control unit  20 . 
     Referring to  FIG. 2 , a perspective view of the oil sensor  18  is generally shown. The oil sensor  18  is a composite sensor assembly that incorporates a number of different sensors. Each of these sensors measures a property of the oil, which is then fed to the control unit  20  for processing and for storage of values in the memory  22 . The physics of the oil sensor  18  are not the subject of this invention. It should be appreciated by those skilled in the art that appropriate sensor technology should be used when performing the method of the inventions disclosed herein. 
     Returning attention to  FIG. 3 , a plot of viscosity as a function of diesel fuel concentration is shown at  24 . The viscosity plot  24  is normalized. The engine oil used to create this viscosity plot  24  has a weight of 15W-40 and is sold under the trademark Shell Rotella. The oil maintained a temperature of 40° Celsius throughout the plot  24 . The viscosity of the oil decreased by 14% after the addition of diesel fuel to represent 5% of the volume of the combined fluid was diesel fuel. The viscosity of the oil declines by 20% as the fuel concentration approaches 8%. In order to safeguard the components of the internal combustion engine  12 , it is desired to detect a fuel leakage before the fuel concentration reaches 8%. Therefore, in the preferred embodiment, the target for the oil sensor  18  is set to detect diesel fuel levels of 5%. 
     Referring to  FIG. 4 , two resistance plots are shown as a function of temperature. A first resistance plot  26  is a graphic representation of the electrical resistance, in mega Ohms as a function of temperature after the internal combustion engine has traveled the equivalent of 2280 miles. A second resistance plot  28  represents the same parameters with the addition of 5% diesel fuel added to the oil. While both resistance plots  26 ,  28  show a decrease in resistance as the temperature increases, the resistance of pure engine oil is always greater than the resistance of the oil/diesel fuel combination at the same temperature. 
     Referring to  FIG. 5 , one embodiment of the inventive method is generally indicated at  30 . The method  30  begins when the internal combustion engine  12  is started at  32 . Once started, an oil level sensor is activated and the output is normalized at  34 . The oil level sensor generates a signal, L, which can be divided into two parts, the true signal l and the error Δl as represented by
 
 L=l±Δl   Equation 1
 
     wherein a typical oil level sensor has a maximum error ratio of Δl/l being equal to approximately 3%. 
     The method  30  then continues to determine whether the oil has been changed at  36 . If the oil has been changed, measurements of oil level L, electrical resistance R, and viscosity υ are taken at  38 . Returning attention to  FIG. 2 , the resistance of engine oil at 75° Celsius decreases by 11% when 5% of the volume of the oil/diesel fuel mixture is attributable to diesel fuel. It is, however, known that adding fresh oil to the crankcase causes the resistance to decrease. In addition, normal engine oil degradation will also cause a reduction in the resistance. Therefore, monitoring resistance R alone cannot specifically detect fuel leakage. The signal measured from the oil condition sensor can be divided into two parts they being
 
 R=r±Δr   Equation 2
 
     wherein, r is the true signal and Δr is the error and Δr/r equals 5%. 
     The signal measured from the viscosity sensor can be divided in two parts, they being
 
ν=ν±Δν  Equation 3
 
     wherein υ is the value for viscosity, Δυ is the error in the signal generated by the viscosity sensor and Δυ/υ should not exceed 5%. Once the viscosity υ and resistant R are measured, their respective inverses are calculated and shall be referred to as K o  and η o , respectively. K o  and η o , along with the oil level L o  are stored in memory  22  at  40 . These are the values against which the operating engine will test the ongoing measured data. 
     As is stated above, the initial values for level L o , the inverse of the resistance K o , and the inverse of viscosity η o  are stored at  40 . The temperature is then measured at  42 . Once the temperature reaches 40° Celsius, the output of the viscosity sensor is normalized at  44  and, when the temperature of the oil reaches 75° Celsius, the output of the resistance sensor is normalized at  46 . The method  30  then compares the current level of oil L against the initial oil level L o  to determine which is greater. If, at  48 , the initial oil level L o  is greater than the current oil level L, it is determined that some of the oil has burned off during normal operation of the internal combustion engine  12 . If this is the case, the original oil level L o  is replaced with the current level L at  50 . Likewise, the original value for the inverse of the resistance K o  is replaced with the calculated inverse of the current resistance at  52  and the calculated inverse of the viscosity η o  is replaced with the current calculated inverse of the measured viscosity at  54 . 
     Once the new initial values are calculated and stored, a cross correlation step for the oil level L and the inverse of the resistance K occurs at  56 . This cross correlation step  56  would occur in the method  30  if it was determined that the original level of oil L o  was equal to or greater than the oil level L, which was determined at step  48 . The cross correlation step  56  is performed because an increase in oil level L could be attributed to either the addition of diesel fuel or the addition of fresh oil. By way of example, adding one quart of fresh oil to a four quart oil pan  16  will increase the oil level L by 33% and increase the inverse of the resistance K by 10%. Therefore, a cross correlation of oil level occurs through the following equations
 
  ω   k   =e   −D|Δl−αΔk|   Equation 4
 
  ω   η   =e   −D|Δl−βΔη|   Equation 5
 
     wherein ω K  and ω η  are the cross correlation function of oil level L and resistance K, and oil level L with viscosity η, respectively. Continuing with equations 4 and 5, above, α is a correlation parameter for the oil level L and resistivity K. β is a correlation parameter for the oil level L and viscosity η. When Δl approaches αΔK, the change in oil level L is related to the change in resistivity K associated with a fuel leakage. Likewise when Δl approaches αΔη, the change in oil level L is related to the change in oil viscosity η associated with a fuel leakage. The correlation functions are close to one whenever the magnitude of the oil level L increase is correlated with the change in resistance Δk or the change in viscosity Δη. These functions effectively suppress the changes in output from the oil level sensor that are not related to fuel leakage. D is a parameter in equations 4 and 5 that controls the damping of the two correlation functions, and varies between 0 and 1. As the value of D increases, the correlation functions decay fast when the oil level L changes are not correlated with a fuel leakage. Through iterative steps, the value of D may be fine tuned. An initial value for D is, however, recommended to be approximately 0.5 for smooth decay of the correlation functions. 
     Once the cross correlation step  56  is completed, a fuel leakage value FL is calculated at  58 . The fuel leakage value FL is calculated using
 
 FL=L×K×η   Equation 6
 
     As diesel fuel leaks into the oil, the oil level L will increase proportionately, the resistance K will decrease and the viscosity η will decrease. The variation of the fuel leakage value FL due to an increase in fluid volume of 5% due to fuel leakage can be calculated as follows: 
     
       
         
           
             
               
                 
                   FL 
                   = 
                   
                     
                       1.05 
                       ⨯ 
                       
                         1 
                         0.89 
                       
                       ⨯ 
                       
                         1 
                         0.86 
                       
                     
                     = 
                     1.37 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   7 
                 
               
             
           
         
       
     
     Thus, there is a 37% increase in the fuel leakage value FL for an additional 5% diesel fuel leakage into the oil. The intrinsic fluctuation of the fuel leakage value FL due to sensor noise can be calculated as follows: 
     
       
         
           
             
               
                 
                   
                     
                       
                         FL 
                         = 
                           
                         ⁢ 
                         
                           L 
                           ⨯ 
                           K 
                           ⨯ 
                           η 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             ( 
                             
                               l 
                               ± 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 l 
                               
                             
                             ) 
                           
                           ⨯ 
                           
                             ( 
                             
                               k 
                               ± 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 k 
                               
                             
                             ) 
                           
                           ⨯ 
                           
                             ( 
                             
                               η 
                               ± 
                               
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 η 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               lk 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               η 
                             
                             ± 
                             
                               ( 
                               
                                 
                                   lk 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   Δ 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   η 
                                 
                                 + 
                                 
                                   k 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   ηΔ 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   l 
                                 
                                 + 
                                 
                                   l 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   ηΔ 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   k 
                                 
                               
                               ) 
                             
                           
                           ± 
                         
                       
                     
                   
                   
                     
                       
                           
                         ⁢ 
                         
                           
                             ( 
                             
                               
                                 l 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 η 
                               
                               + 
                               
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 η 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 l 
                               
                               + 
                               
                                 η 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 l 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 k 
                               
                             
                             ) 
                           
                           ± 
                           
                             ( 
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               l 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               k 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               η 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   8 
                 
               
             
           
         
       
     
     Since (lΔkΔη+kΔηΔl+ηΔlΔk) and ΔlΔkΔη are relatively small, Equation 8 simplifies to 
     
       
         
           
             
               
                 
                   FL 
                   = 
                   
                     
                       
                         lk 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         η 
                       
                       ± 
                       
                         ( 
                         
                           
                             lk 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             Δ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             η 
                           
                           + 
                           
                             k 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             ηΔ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             l 
                           
                           + 
                           
                             l 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             ηΔ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             k 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                         lk 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         η 
                       
                       + 
                       
                         Δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           FL 
                           . 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   9 
                 
               
             
           
         
       
     
     The intrinsic fluctuation of fuel leakage, ΔFL, as a percentage of lkη can be calculated using 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             Δ 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             FL 
                           
                           
                             lk 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             η 
                           
                         
                         = 
                         
                           
                             ( 
                             
                               
                                 lk 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 η 
                               
                               + 
                               
                                 k 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 η 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 Δ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 l 
                               
                               + 
                               
                                 l 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 ηΔ 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 k 
                               
                             
                             ) 
                           
                           
                             lk 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             η 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               η 
                             
                             η 
                           
                           + 
                           
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               l 
                             
                             l 
                           
                           + 
                           
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               k 
                             
                             k 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           ( 
                           
                             
                               5 
                               ⁢ 
                               % 
                             
                             + 
                             
                               3 
                               ⁢ 
                               % 
                             
                             + 
                             
                               5 
                               ⁢ 
                               % 
                             
                           
                           ) 
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           13 
                           ⁢ 
                           
                             % 
                             . 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   10 
                 
               
             
           
         
       
     
     As is shown by equations 7 and 10, the increase of the fuel leakage value FL due to 5% increase in volume due to fuel leakage is almost three times greater than the intrinsic noise of the oil sensor  18 . With the cross correlation values, the fluid level value FL can be calculated using
 
 FL=L ×(  ω   k   ×K )×(  ω   η ×η)  Equation 11.
 
     Once the fuel leakage value FL is calculated using the cross correlation functions (equations 4 and 5, above), it can be determined whether the fuel leakage value FL is greater than a predetermined value or threshold at  60 . Because the fuel leakage FL for a 5% fuel leakage is 1.37, a warning threshold should be set at a value smaller than 1.37 e.g., 1.20. If the fuel leakage value FL is greater than the warning threshold, a warning is indicated at  62 . If not, it is determined whether the internal combustion engine  12  is turned off at  64 . If not, the method iteratively loops back to step  42  where the temperature is measured. 
     Since the physical and chemical properties of the oil would change gradually and continuously due to aging effects of normal wear, the references L o , K o  and η o  saved in memory  22  have to be reset periodically. Under normal engine operation, the oil level L would drop slowly due to the loss or burning of engine oil in the internal combustion engine  12 . If the measured oil level L continues to decline, there should not be any significant diesel fuel leakage. Therefore, it should be appropriate to reset all of the references L o , K o  and η o  in steps  50 ,  52 ,  54  respectively. As mentioned previously, the oil sensor  18  may have a level output that could have a plus or minus 3% error. Therefore, the fact that the oil level L is less than the reference for the oil level L o  does not necessarily mean the oil level  14  in the oil pan  16  is actually less than the reference L o . 
     In order to prevent this uncertainty, an alternative embodiment to step  48  in  FIG. 5  is graphically represented in  FIG. 6 . The alternative method for resetting the references is generally indicated at  64 . The method begins by identifying a number n that will indicate the number of iterations in which the measurements for the oil level  14  are taken. A first oil level measurement L n  is taken and measured to determine whether it is less than the reference oil level L o . This step occurs at  66 . The iterative oil level measurement L n  is stored at  68 . The counter n is increased by 1 at  70 . It is then determined whether n has reached a limit x at  72 . If not the alternative method  64  is released and the measurement method  30  is continued. If the counter has reached its limit x, and if at  74 , one half of the iterative oil level measurements L n  are less than the reference level L o , the reference level L o  is redefined as the average of all of the iterative level measurements L n . This step occurs at  76 . 
     Referring now to  FIG. 7 , a method is generally indicated at  76  that is used to detect when a massive fuel leak occurs. During operation of the internal combustion engine  12 , a massive fuel leakage could occur due to the high pressure existing in fuel rails (not shown). When the motor vehicle  10  is running, oil is not typically added to the oil pan  16 . In addition, normal engine oil degradation would not cause any significant short term changes in oil resistance K. Without the interference of these two factors, measuring the resistance K alone is enough to detect a massive instantaneous fuel leakage. In the method  76 , temperature and resistance of the oil are measured at  78 . The resistance is compensated with a temperature coefficient and then normalized with respect to its previous value at  80 . It is then determined whether the normalized compensated resistance R t  is greater than a predetermined threshold T t  at  82 . If so, it is indicated that a massive fuel leak has occurred at  84 . If not, the method  76  loops back and continues to measure the temperature and resistance at  78 . This method continues during the total operation of the internal combustion engine  12 . 
     The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. 
     Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.