Abstract:
A method and control module for indicating engine oil life includes a viscosity determination module determining a viscosity of the engine oil based on an engine oil pressure and engine oil temperature. The control system further includes a comparison module comparing the viscosity of the engine oil to a threshold and generating a warning signal in response to comparing the viscosity.

Description:
FIELD 
     The present disclosure relates to vehicle control systems and more particularly to a system and method for estimating engine oil life based on viscosity. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. The background information provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Motorized vehicles may include a powertrain that includes a powerplant (e.g., an engine, an electric motor, and/or a combination thereof), a multispeed transmission, and a differential or final drive train. The powerplant may include an engine that produces drive torque that is transmitted through one of various gear ratios of the transmission to the final drive train to drive wheels of the vehicle. 
     Engine oil is used to lubricate the components in the engine. Engine oil deteriorates with use. Engine oil must therefore be replaced. Traditionally, engine oil was changed whenever the vehicle reached a predetermined mileage, or a specified duration, which ever comes first. Under severe operating conditions, however, vehicle manufacturers may suggest that the engine oil be changed more frequently. These situations require the operator of the vehicle to make a judgment as to when to change the engine oil. Other manufacturers provide a system for determining engine oil life. One example of an engine oil life system is the General Motors (GM) Engine Oil Life System (EOLS). EOLS keeps track of the various operating conditions of the vehicle and adjusts the mileage between oil changes. EOLS is responsible for determining the percentage remaining life of the engine oil and whether the engine oil needs to be changed. Excessive degradation of the engine oil occurs at its temperature extremes. At high oil temperatures, antioxidants in the oil tend to become depleted, and the oil becomes more viscous and acidic due to oxidation. At low oil temperatures, fuel, water and soot tend to accumulate in the oil, reducing its viscosity and increasing wear. Letting a driver to take into consideration these conditions is not practical. Even with these factors, certain conditions are not considered. 
     SUMMARY 
     The present disclosure increase provides a system and method for increasing the accuracy of predicting oil life between the oil change indicators. The present disclosure uses viscosity to improve the oil life indication. Too high oil viscosity will result in too high oil pressure build up and hampers sufficient oil flow to supply fresh lubricant to critical areas of the engine, and accelerated wear will result. Too low oil viscosity will results in poor hydrodynamic lubrication of the loaded surfaces. Therefore, the “viscosity of oil” improves the oil life determination. 
     In one aspect of the disclosure, a method includes determining an engine oil pressure, determining an engine oil temperature, determining a viscosity of the engine oil based on the engine oil pressure and engine oil temperature, comparing the viscosity of the engine oil to a threshold, and generating a warning signal in response to comparing the viscosity. 
     In another aspect of the disclosure, a method includes determining a new oil viscosity, determining a used oil viscosity, when a ratio of a used oil viscosity and the new oil viscosity is outside a range, generating an indicator corresponding to oil life. 
     In a further aspect of the disclosure, a control module for indicating engine oil life includes a viscosity determination module determining a viscosity of the engine oil based on n engine oil pressure and engine oil temperature. The control system further includes a comparison module comparing the viscosity of the engine oil to a threshold and generating a warning signal in response to comparing the viscosity. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of an engine and engine control system; 
         FIG. 2  is a functional block diagrammatic view of an oil lubricating system for the engine of  FIG. 1 ; 
         FIG. 3  is a plot oil pressure versus engine speed at a constant temperature. 
         FIG. 4  is a plot of vehicle speed, oil pressure, oil temperature, engine speed for a test engine. 
         FIG. 5  is a plot of vehicle speed, oil temperature and oil viscosity index versus time; 
         FIG. 6  is a plot of engine speed, oil temperature and viscosity index at idle during a test cycle; 
         FIG. 7  is a plot of an oil viscosity indicator versus the oil temperature during a driving cycle; 
         FIG. 8  is a plot of oil pressure versus engine speed at different oil temperatures; 
         FIG. 9  is a plot of oil viscosity versus oil temperature for an engine below 800 RPM&#39;s of crankshaft speed; 
         FIG. 10  is a block diagram of the control system of  FIG. 1  for performing the method of the present disclosure; and 
         FIG. 11  is a flowchart of a method for performing the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary engine control system  10  is schematically illustrated in accordance with the present disclosure. The engine control system  10  includes an engine  12  and a control module  14 . The engine  12  includes an intake manifold  15 , a fuel injection system  16  having fuel injectors and an exhaust system  17 . The system  10  may also include a turbocharger  18 . The exemplary engine  12  includes six cylinders  20  configured in adjacent cylinder banks  22 ,  24  in a V-type layout. Although  FIG. 1  depicts six cylinders (N=6), it can be appreciated that the engine  12  may include additional or fewer cylinders  20 . For example, engines having 2, 4, 5, 8, 10, 12 and 16 cylinders are contemplated. It is also anticipated that the engine  12  can have an inline-type cylinder configuration. While a gasoline powered internal combustion engine utilizing direct injection is contemplated, the disclosure may also apply to diesel or alternative fuel sources. 
     During engine operation, air is drawn into the intake manifold  15  by the inlet vacuum created by the engine intake stroke. Air is drawn into the individual cylinders  20  from the intake manifold  15  and is compressed therein. Fuel is injected by the injection system  16 . The air/fuel mixture is compressed and the heat of compression and/or electrical energy ignites the air/fuel mixture. Exhaust gas is exhausted from the cylinders  20  through exhaust conduits  26 . The exhaust gas drives the turbine blades  25  of the turbocharger  18  which in turn drives compressor blades  25 . The compressor blades  25  can deliver additional air (boost) to the intake manifold  15  and into the cylinders  20  for combustion. 
     The turbocharger  18  can be any suitable turbocharger such as, but not limited to, a variable nozzle turbocharger (VNT). The turbocharger  18  can include a plurality of variable position vanes  27  that regulate the amount of air delivered from the vehicle exhaust  17  to the engine  12  based on a signal from the control module  14 . More specifically, the vanes  27  are movable between a fully-open position and a fully-closed position. When the vanes  27  are in the fully-closed position, the turbocharger  18  delivers a maximum amount of air into the intake manifold  15  and consequently into the engine  12 . When the vanes  27  are in the fully-open position, the turbocharger  18  delivers a minimum amount of air into the engine  12 . The amount of delivered air is regulated by selectively positioning the vanes  27  between the fully-open and fully-closed positions. 
     The turbocharger  18  includes an electronic control vane solenoid  28  that manipulates a flow of hydraulic fluid to a vane actuator (not shown). The vane actuator controls the position of the vanes  27 . A vane position sensor  30  generates a vane position signal based on the physical position of the vanes  27 . A boost sensor  31  generates a boost signal based on the additional air delivered to the intake manifold  15  by the turbocharger  18 . While the turbocharger implemented herein is described as a VNT, it is contemplated that other turbochargers employing different electronic control methods may be employed. 
     A manifold absolute pressure (MAP) sensor  34  is located on the intake manifold  15  and provides a (MAP) signal based on the pressure in the intake manifold  15 . A mass air flow (MAF) sensor  36  is located within an air inlet and provides a mass air flow (MAF) signal based on the mass of air flowing into the intake manifold  15 . The control module  14  uses the MAF signal to determine the A/F ratio supplied to the engine  12 . An RPM sensor  44  such as a crankshaft position sensor provides an engine speed signal. An intake manifold temperature sensor  46  generates an intake air temperature signal. The control module  14  communicates an injector timing signal to the injection system  16 . A vehicle speed sensor  49  generates a vehicle speed signal. 
     The exhaust conduits  26  can include an exhaust recirculation (EGR) valve  50 . The EGR valve  50  can recirculate a portion of the exhaust. The controller  14  can control the EGR valve  50  to achieve a desired EGR rate. 
     The control module  14  controls overall operation of the engine system  10 . More specifically, the control module  14  controls engine system operation based on various parameters including, but not limited to, driver input, stability control and the like. The control module  14  can be provided as an Engine Control Module (ECM). 
     The control module  14  can also regulate operation of the turbocharger  18  by regulating current to the vane solenoid  28 . The control module  14  can communicate with the vane solenoid  28  to provide an increased flow of air (boost) into the intake manifold  15 . 
     An exhaust gas oxygen sensor  60  may be placed within the exhaust manifold or exhaust conduit to provide a signal corresponding to the amount of oxygen in the exhaust gasses. 
     Referring now to  FIG. 2 , a block diagrammatic view of an engine oiling system  80  is illustrated. The engine oiling system  80  includes an oil sump  82  that is typically located at the bottom of the engine. An engine oil pick-up tube  84  draws oil therein due to the action of a pump  86 . The pump  86  draws oil from the sump  82  through the pick-up tube  84  and into an oil filter  88 . The oil filter  88  provides fluid to oil galleries  90  for lubricating various portions of the engine  12  including the bearings, pistons, rods and other internal components of engine  12 . From the galleries  90  the oil returns to the sump  82 . 
     The pump  86  may be different types of pump including a gear-type positive displacement pump or a vane-type variable displacement pump. For a displacement pump, a relief valve  92  is used to recirculate the excessive oil outside of the hot idling operation. The waste oil recirculating through the relief valve  92  may ultimately reduce the overall fuel economy of the vehicle since an excessive amount of energy is used to drive the positive displacement pump. 
     A pressure sensor  94  in communication with the oil between the oil filter  88  and the oil galleries  90  generates an oil pressure signal. A temperature sensor  96  in communication with the oil in the sump provides an engine oil temperature signal. 
     The engine oil pressure is caused by the resistance of the oil to flow under the pumping action of the oil pump. The higher the oil viscosity, the higher the resistance to oil flow. The oil pressure is a measure of the oil&#39;s resistance to flow. The oil pressure in the engine oiling system is a function of two factors: oil viscosity and oil flow rate. Most current engines today are a positive displacement type. 
     The pump  86  may also be a variable displacement lubricating oil pump used to minimize the waste of oil recirculation due to inherent capability of delivering right amount of oil flow at various operating conditions. 
     The oil flows in an engine may be unregulated until a certain flow, then regulated thereafter. For both positive and variable displacement type pumps, in general, the oil flow rates are proportional to the speed (RPM) of the oil pump when the oil flow is not regulated. The oil pumps are directly coupled with engine speed and the speed of the oil pump directly relates with the engine RPM. Therefore, for a given engine speed (RPM) such as at idle, the oil flow rate is nearly constant and the oil pressure is mainly a function of oil viscosity. However, the oil viscosity is sensitive to temperature of the oil. The viscosity of oil decreases as the temperature of the oil increases. Since the oil viscosity is the driving force to resist flow, the oil pressure tends to decreases as the oil temperature increases. Conversely, as the oil temperature decreases, oil pressure in the oiling system increases. Therefore, by measuring the oil pressure and the oil temperature, a relationship between the oil viscosity and the oil pressure can be built. 
     For regulated oil flow, the pump tries to maintain preset pressure at its outlet by adjusting its delivery flow in accordance with the system requirements. If pressure differential across the pump is less than the setting pressure, the pump outputs its maximum delivery corrected for internal leakage. After the pressure setting has been reached, the output flow is regulated to maintain preset pressure by changing the pump&#39;s displacement. The displacement can be changed from its maximum value down to zero, depending upon the downstream oil pressure. The pressure range between the preset pressure and the maximum pressure, at which the displacement is zero, is referred to as a regulation range. From the pump characteristics including the relationship between the displacement and the oil pressure, the oil flow rates can be determined even in the oil regulation range. 
     As the volume of oil pumped into the engine increases, the oil pressure increases. Oil pressure is a function of two factors for a given engine: oil viscosity and oil flow rate. The oil flow in oil galleries is typically laminar. For laminar flow in a channel, the total pressure drop, ΔP, is linearly proportional to the product of the oil flow rate, Q, and the oil viscosity, μ
 
ΔP≈Q×μ  (1)
 
From Eqn. (1), the oil viscosity, μ, becomes
 
                   μ   ≈       Δ   ⁢           ⁢   P     Q             (   2   )               
The oil flow rate, Q, is a function of engine RPM, ω, and oil flow regulation.
 
     For an unregulated oil flow, most oil pumps behave as a positive displacement pump. The oil flow rate of such positive displacement pumps is proportional to the rotational speed (RPM) of the oil pump. Since the oil pump speed is directly proportional to engine speed, ω, the oil viscosity, μ, is simply a function of oil pressure and engine RPM, ω, 
     
       
         
           
             
               
                 
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                       Δ 
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                       ⁢ 
                       P 
                     
                     ω 
                   
                 
               
               
                 
                   ( 
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     For regulated oil flow, the oil flow rate, Q, depends on both engine RPM and the oil pressure. The oil flow rate, Q, to engine gallery in Eqn. (2) has to be modified by the amount of the regulated oil flow rate. The amount of regulation depends on an oil pump characteristics of a particular pump type. The regulated oil flow rate can be approximated by modeling the regulated oil flow rate, f, as a function of oil pressure and engine RPM,
 
Q≈Q unregulated −f(ΔP, ω)   (4)
 
     Once the oil pump characteristics are known, such as the relationship between the regulated oil flow rate and the oil pressure, and the pump speed, Eqn. (2) can be applied to wide range of engine operating conditions beyond unregulated region. 
     Referring now to  FIG. 3 , to validate Eqn. (3), a spin-stand test data using a GM 4.2 L, L6 engine were used to plot the relationship between the oil pressure and the engine RPM at a constant oil temperature 120° C. As shown in  FIG. 2 , the oil pressure increases linearly with the engine RPM until the relief valve starts open near the oil pressure 60 psi. Higher oil pressures above 60 psi, the oil flow starts to regulate through the relief valve and the oil pressure deviates from the linear relationship. In order to apply to more realistic engine operating conditions, the engine chassis dynamometer was operated using the Federal Test Procedure (FTP) test for city driving cycle.  FIG. 4  shows the variations of the vehicle speed, engine RPM and also corresponding oil pressure fluctuations and the oil temperature variations in the oil sump. As shown in  FIG. 5 , the oil pressure fluctuates largely due to engine RPM variation during the acceleration and the deceleration.  FIG. 5  shows the oil viscosity indicator which is the oil pressure divided by the engine RPM from Eqn. (3) as signal  110 . The oil viscosity indicator is fluctuating during FTP cycle as the oil flow is regulated through the relief valve at high engine RPM and the oil flow circuit in engine galleries varies due to variable valve actuations. To avoid these complexities, only the data during idle conditions were utilized as the oil flow circuit is steady and not regulated. As shown in  FIG. 6 , the oil viscosity indicator values are vary stable and does not fluctuate during the engine idle speed. The averages values of the oil viscosity indicator at 13 idle conditions were plotted as a function of oil temperature in  FIG. 7 . The 13 data points for the oil viscosity indicator falls closely along the linear relationship between the oil viscosity and the oil temperature for the narrow oil temperature range available in the test between 85° C. and 95° C. 
     In order to apply the present invention to variable displacement pumps, a GM LT8, Gamma engine was utilized. The relationship between the oil pressure and the engine RPM is shown in  FIG. 8  at five different oil temperatures. For oil pressures below 230 Kpa, the oil flow is not regulated. The oil flow starts to regulate when the oil pressure is higher than 230 Kpa. As shown in  FIG. 8 , the relationship between the oil pressure and the engine RPM is linear for the unregulated oil flow region when the oil pressure is below 230 Kpa and the data deviates from a linear relationship when the oil pressure is greater than 230 Kpa. Therefore, Eqn. (3) can still be applied to a variable displacement pump when the oil flow is not regulated. The engine test data at low engine RPM&#39;s (below 810) were selected to evaluate the oil viscosity indicator based on Eqn. (3). The averaged values of these engine test data were plotted as a function of the oil temperature, as shown in  FIG. 9 . Although the test data for 50° C. oil temperature in the plot is included, the oil flow is already regulated at this low oil temperature and this data point is not valid to estimate the oil viscosity. As shown in  FIG. 9 , the oil viscosity indicator values from Eqn. (3) are scaled with a constant, k2, to compare directly with the viscosity values of 5W30 engine oil. The scaled oil viscosity from Eqn. (3) falls very closely with the measured oil viscosity. However, as expected, it deviates from the measured oil viscosity at a low oil temperature, 50° C., as the oil flow is regulated. In order to determine viscosity in a regulated region, Eqn. (2) is used with Eqn. (4) to take into account the corrected amount of oil flow. 
     Referring now to  FIG. 10 , a simplified block diagrammatic view of the components of the control module  14  for engine oil monitoring is illustrated. Each of the modules within the control module  14  may be interconnected. The control module  14  may include various modules therein to perform the method of the present disclosure. 
     The control module  14  may be in communication with a reset  210 . The reset  210  may be a reset switch or other type of reset interface. A reset switch may, for example, be located on the instrument panel. The reset switch may be a combination of switches that are activated in a certain sequence to generate a signal as an indicator that the oil has been changed in the vehicle. 
     The control module  14  may include an oil change determination module  212  that receives the reset signal from the reset  210 . 
     An engine oil temperature determination module  214  receives a temperature signal from the temperature sensor  96  and provides the temperature signal to various other modules within the control module  14 . An engine oil pressure determination module  215  receives an oil pressure sensor signal from the oil pressure sensor  94  and provides the oil pressure signal to other modules within the control module  14 . An engine speed determination module  216  provides an engine speed signal to the oil flow rate determination module  218 . The oil flow rate determination module  218  may also receive a signal from the unregulated oil flow determination module  220 . Based on the oil flow rate signal generated at the oil flow rate determination module  218 , a viscosity signal may be generated by a viscosity determination module  222 . The viscosity determination module  222  may determine the viscosity and correlate the viscosity with the temperature. The viscosity determination module output may store a new oil viscosity in a memory  224 . Thus, when the reset switch is first reset, the engine oil is new and thus a new oil viscosity determination is made and stored in the new oil viscosity memory  224 . 
     The viscosity determination module  222  may also be in communication with a viscosity comparison module  226 . The viscosity comparison module may compare the new oil viscosity and the viscosity of the used oil from the viscosity determination module  222 . By comparing the ratio of the used viscosity and new viscosity to a threshold, an indicator  228  may be used to indicate whether or not an oil change is required. The viscosity comparison module  226  may compare an upper constant and a lower constant to the ratio of the used viscosity and new viscosity. When the viscosity is between the two constants, the viscosity is within range and the indicator  228  is not activated. When the viscosity is either above or below the outer constant, the viscosity comparison module  226  may activate the indicator  228 . The indicator  228  may provide an indication that an oil change is due or that the oil has an amount of predetermined life. Of course, having two constants is merely one example provided by the present disclosure. A variation of the present disclosure may use only one constant. 
     Referring now to  FIG. 11 , a method of controlling an engine around an intrusive diagnostic procedure is set forth. As mentioned above, oil pressure is the result of the resistance of the oil to flow under a pumping action. Besides oil viscosity, changes in the oil galleries may also affect the resistance and thus the measured oil pressure. Smaller oil flow passages provide more resistance to oil flow, and therefore higher oil pressure and, conversely, large oil flow passages provide less resistance, resulting in lower oil pressure. For example, worn out bearings can result in low oil pressure. The procedure described in this section is applicable to different oil types and engine types. Wear in engine bearings during an oil change interval is presumed to be small and its effect on the oil pressure is negligible. However, the change over multiple oil change intervals can be large with no loss of accuracy. 
     In step  310  whether the vehicle engine is on is determined. This can be determined from a signal from the engine control module. The system does not proceed when the engine is not on or running. In step  312  whether the engine has recently had an oil change is determined. The reset  210  of  FIG. 10  may be used to determine a reset. If there has been an oil change in step  312 , whether the engine oil pressure is unregulated is determined in step  314 . This may be determined by measuring the oil pressure and oil temperature by oil the temperature and pressure sensors located downstream of the oil filter illustrated in  FIG. 2 . When the oil flow is unregulated in step  314 , the oil flow rate is directly related to the engine speed in step  316 . The oil pressure and the engine RPM are measured and the oil viscosity indicator is calculated from Eqn. (3). In step  318  the viscosity and oil temperature are correlated. Adjustments may be made to the viscosity in view of the temperature. The fresh oil viscosity indicator, μ new , of the new oil is then registered or stored in a memory for future comparison with the used oil viscosity in step  320 . 
     When the oil flow is regulated (not unregulated) in step  314 , the correct oil flow is estimated from Eqn. (4) and the oil viscosity indicator is calculated from Eqn. (2) in step  322 . Steps  318  and  320  are then also performed as describe above. It is also noted that the steps  314 - 320  are only performed after it has been determined that an oil change has taken place. 
     Referring back to step  312 , when an oil change has not taken place, step  330  determines whether engine oil pressure is unregulated. This is accomplished by measuring the oil pressure and oil temperature using the engine temperature and pressure sensors. When it is determined that the oil flow is unregulated in step  330 , the oil flow rate and engine speed are related in step  332  and thus the engine speed is used to determine the used oil viscosity indicator, μ old , by the same procedure as that described above for fresh oil in steps  316 - 318 . Step  334  adjusts the viscosity for the oil temperature. When the used oil viscosity indicator, μ used , has been calculated in step  334 , it is compared to the fresh oil viscosity, μ new , by, for example, forming a ratio by dividing μ used  by μ new  in step  336 . In step  336  the ratio of viscosities is compared to a predetermined range defined by a lower constant C 1  and an upper constant C 2 . The constants may be determined experimentally and depend on the oil properties. If the compared ratio value is outside the range defined by C 1  and C 2 , an oil change signal is generated in step  338 . A “change oil” warning signal may be sent to the vehicle operator when the viscosity estimated at a given oil temperature and engine speed exceeds a predetermined “threshold” or range as set forth above. In step  336  if the ratio is within the range in step  340 , no oil change signal is generated since the viscosity is good. 
     Referring back to step  330 , when the oil flow is regulated (not unregulated), the correct oil flow is estimated from Eqn. (4) and the oil viscosity indicator is calculated from Eqn. (2) in step  350 . Steps  334  and  340  are then also performed as describe above. 
     Oil changes based on the present invention provide a means for achieving improved engine operational efficiency, more effective maintenance schedules, and extended engine life, all of which result in lower operational costs. In addition, the oil viscometer can protect against engine damage by warning the driver of sudden oil loss, or accelerated oil deterioration. Finally, oil changes based on the present disclosure may help to reduce the environmental cost of vehicle operation by extending the oil change interval. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.