Abstract:
An engine oil system comprises an oil condition sensing device and a control module. The oil condition sensing device includes an electrically actuated member and is in fluid communication with an engine oil reservoir. The control module selectively causes current to be supplied to the oil condition sensing device to actuate the member, measures the current, determines a parameter of the current, and selectively identifies at least two of an oil level, an oil change event, and an oil viscosity level based on the parameter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/023,954, filed on Jan. 28, 2008. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to electrical systems and methods for engine oil measurements. 
     BACKGROUND 
     The background description 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. 
     Motor oil is a type of liquid oil used for lubrication by various types of motors. In particular, internal combustion engines use motor oil to provide lubrication between mechanical components. The motor oil also cools the engine by dissipating heat generated by friction between the mechanical components. 
     Awareness of engine oil viscosity, engine oil levels, and engine oil change events has become increasingly important to engine control systems. This is due to recent advancements in engine control strategies that use engine oil for precise timing. Such control strategies include, for example, cam phasing, active fuel management, and two-step valve actuation. Implementing multiple systems, one for each of the detection of engine oil viscosity, the detection of engine oil levels, and the detection of an engine oil change event can be complex and expensive. 
     SUMMARY 
     An engine oil system comprises an oil condition sensing device and a control module. The oil condition sensing device includes an electrically actuated member and is in fluid communication with an engine oil reservoir. The control module selectively causes current to be supplied to the oil condition sensing device to actuate the member, measures the current, determines a parameter of the current, and selectively identifies at least two of an oil level, an oil change event, and an oil viscosity level based on the parameter. 
     A method comprises selectively causing current to be supplied to an oil condition sensing device to actuate a member of the oil condition sensing device; measuring the current supplied to the oil condition sensing device; determining a parameter of the current; and selectively identifying at least two of an oil level, an oil change event, and an oil viscosity level based on the parameter. 
     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 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 exemplary engine system according to the principles of the present disclosure; 
         FIG. 2  graphically depicts three exemplary traces of the current of a solenoid according to the principles of the present disclosure; 
         FIG. 3  is a functional block diagram of an exemplary solenoid system according to the principles of the present disclosure; 
         FIG. 4  is a flowchart depicting exemplary steps performed in analyzing the current signal of a solenoid according to the principles of the present disclosure; 
         FIGS. 5A and 5B  are cross-sectional views of an exemplary implementation of the solenoid assembly according to the principles of the present disclosure; 
         FIG. 6A  is a cross-sectional view graphically illustrating a solenoid according to the principles of the present disclosure when the oil level is above the low oil level; 
         FIG. 6B  shows exemplary historical traces of solenoid notch times according to the principles of the present disclosure; 
         FIG. 7A  is a cross-sectional view graphically illustrating a solenoid according to the principles of the present disclosure after an oil change; 
         FIG. 7B  shows an exemplary historical trace of solenoid notch times according to the principles of the present disclosure; 
         FIG. 8A  is a cross-sectional view graphically illustrating a solenoid according to the principles of the present disclosure when the oil level is below the low oil level; 
         FIG. 8B  shows an exemplary historical trace of solenoid notch times according to the principles of the present disclosure where an oil change was performed after the oil level had fallen below the low oil level; 
         FIG. 9A  is a cross-sectional view graphically illustrating a solenoid according to the principles of the present disclosure when the oil level is below the critical oil level; 
         FIG. 9B  shows an exemplary historical trace of solenoid notch times according to the principles of the present disclosure; 
         FIG. 10  is a graphical illustration of notch delay times over a number of solenoid cycles according to the principles of the present disclosure that indicate an oil change event; 
         FIG. 11  is a table of exemplary determinations made for various solenoid response measurements according to the principles of the present disclosure; 
         FIG. 12  is a functional block diagram of an exemplary implementation of the oil diagnosis module of  FIG. 1  according to the principles of the present disclosure; and 
         FIG. 13  is a flowchart that depicts exemplary operation of the notch analysis module of  FIG. 12  according to the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     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 , a functional block diagram of an exemplary engine system  100  is presented. The engine system  100  includes an engine  102 , an engine control module  104 , an oil diagnosis module  106 , and an oil reporting module  108 . The engine control module  104  controls operation of the engine  102 . For example, the engine control module  104  may control actuators (not shown) within the engine  102  to produce a torque as requested by a driver. 
     The engine  102  includes an oil sump  110  that stores oil used for lubricating and cooling the engine  102 . The oil sump  110  may be located at the bottom of the engine  102  so that gravity returns oil to the oil sump  110 . A solenoid assembly  112  measures characteristics of the oil in the engine system  100 . For example only, the solenoid assembly  112  may be located within the oil sump  110 . 
     The oil diagnosis module  106  uses the solenoid assembly  112  to determine oil conditions. As described below in  FIG. 2 , the current draw of a solenoid changes depending on the viscosity of the oil. The oil diagnosis module  106  may therefore be able to determine viscosity of the oil using the solenoid assembly  112 . In addition, the solenoid assembly  112  may be arranged such that the solenoid interfaces with air when the oil level becomes low. This may appear as a dramatic decrease in oil viscosity. Further, the solenoid assembly  112  may be linked to a drain plug of the oil sump  110  so that the solenoid assembly  112  will recognize an oil change event. 
     In brief,  FIG. 2  depicts exemplary traces of current of a solenoid when presented with fluids having different viscosities. An exemplary system for measuring these currents is shown in  FIG. 3 .  FIG. 4  depicts exemplary steps used to analyze the current signal to produce a number, which may be indicative of viscosity.  FIGS. 5A-5B  depict an exemplary implementation of the solenoid assembly  112 , where a column of oil connected to the drain plug allows for detection of oil change events. 
       FIGS. 6A-9B  depict exemplary oil conditions measured by the solenoid assembly.  FIG. 10  depicts a graph of solenoid response versus time that indicates an oil change has occurred.  FIG. 11  depicts how solenoid readings can be interpreted according to one exemplary implementation.  FIG. 12  is a block diagram of an exemplary implementation of the oil diagnosis module of  FIG. 1 , and  FIG. 13  depicts exemplary steps performed by the oil diagnosis module. 
     Referring back to  FIG. 1 , the oil diagnosis module  106  provides oil status information to the engine control module  104 . For example, this oil status may include oil viscosity, oil level, and detection of oil-related events. For example, the oil diagnosis module  106  may detect oil change events, oil drain events, and oil fill events. The engine control module  104  may modify operation of the engine  102  based on this information. For example, as the oil viscosity increases, the engine control module  104  may limit the speed of the engine  102 . 
     The engine control module  104  may also report oil information to the oil reporting module  108 . The oil reporting module  108  may provide visual and/or auditory indicators of oil status to the driver of the vehicle. The oil reporting module  108  may track and estimate the condition of the oil. This estimation may be based upon the number of miles driven since the last oil change. The estimation may be adjusted based on measured oil viscosity from the oil diagnosis module  106 . 
     When an oil change has been performed, this event may be reported to the oil reporting module  108  by a driver or technician through a user interface. This user interface may be multiplexed with other vehicle controls, such as odometer and/or clock controls. Inadvertent indications of an oil change to the oil reporting module  108  may be identified by comparing user entered data to oil change events detected by the oil diagnosis module  106 . Alternatively, the oil reporting module  108  may ignore user input and determine oil change events based on data from the oil diagnosis module  106 . The oil reporting module  108  may indicate to the driver that an oil change is needed. 
     Referring now to  FIG. 2 , three exemplary traces  202 ,  204 , and  206  of the current of a solenoid are shown. Trace  202  corresponds to a low viscosity, trace  204  corresponds to a higher viscosity, and trace  206  corresponds to an infinite viscosity. An infinite, or extremely high, viscosity has the same effect as if the armature of the solenoid were mechanically stuck. Traces  202  and  204  each include a notch in the current. By contrast, trace  206  lacks the notch. For traces similar to trace  206 , the notch time may be considered to be infinite, or set to a maximum amount of time. 
     The location of the notch is an indication of the viscosity of the fluid with which the solenoid is interfacing. Because the solenoid piston displaces fluid in front of the piston, hydraulic resistance is caused by the viscous oil moving through restrictive oil flow passages (such as one or more orifices). This hydraulic resistance exerts a pressure on the face of the piston, which resists armature movement and changes the current response characteristics of the solenoid. 
     At a start point  210 , the solenoid is instructed to actuate. This may be initiated by a trigger signal that arrives at the start point  210 . For purposes of illustration, trace  202  will be analyzed. After the start point  210 , the current of trace  202  begins increasing. At a first point  212 , trace  202  transitions from increasing to decreasing. The first point  212  is therefore a local maximum. 
     Trace  202  then decreases until a second point  214 , when trace  202  transitions from decreasing back to increasing. The second point  214  is therefore a local minimum. The armature of the solenoid begins moving at the first point  212  and stops moving at the second point  214 . The measured current between the first and second points  212  and  214  decreases because the moving armature creates a back electromotive force (EMF) that opposes the electrical potential. The amount of time elapsed between the start point  210  and the second point  214  is referred to as the notch time. The notch time of trace  202  is less than the notch time of trace  204 , indicating that the solenoid is interfacing with a higher viscosity fluid in trace  204 . The notch time of trace  206  may be set to a predetermined maximum value. For example, the notch time for trace  206  may be set to 45 ms. 
     Referring now to  FIG. 3 , a functional block diagram of an exemplary solenoid system is presented. A solenoid  300  receives power from a voltage supply  302 . For example only, the voltage supply  302  may provide a constant voltage to the solenoid  300 . The current from the voltage supply  302  may be limited to prevent damage to the solenoid  300 . 
     A solenoid control module  304  controls when the solenoid  300  is actuated. In various implementations, the solenoid  300  may include a spring that displaces an armature of the solenoid  300  to a first position. By providing a current through windings of the solenoid  300 , electromagnetic force generated by current can displace the armature against the spring to a second position. When the current is removed, the armature may return to the first position by action of the spring. 
     The solenoid control module  304  may activate a switch  306  in order to actuate the solenoid  300 . The switch  306  may conduct current between the solenoid  300  and a reference potential, such as ground. When current is flowing through the switch  306 , the solenoid  300  may be considered actuated, with the armature at the second position. 
     For example only, the switch  306  may include an n-channel metal oxide semiconductor field effect transistor (MOSFET). The transistor may include a control terminal (labeled G or gate) and first and second terminals (labeled D and S for drain and source, respectively). The control terminal may be connected to the solenoid control module  304 , the first terminal may be connected to the solenoid  300 , and the source terminal may be connected to the reference potential via a shunt resistor  310 . 
     Current flowing through the solenoid  300  therefore flows through the resistor  310 , creating a voltage drop across the resistor  310  that is proportional to the amount of current. This voltage drop may be measured by a voltage amplifier  312 , which may be referenced to the same reference potential. Alternatively, any other system for sensing current may be used, such as a Hall effect sensor. 
     An amplified version of the input voltage is output from the voltage amplifier  312  to an analog-to-digital (A/D) converter  314 . The A/D converter  314  digitizes the output of the voltage amplifier  312  and outputs a digital signal. This digital signal can then be analyzed to determine the notch time of the solenoid&#39;s current. A current measurement module  316  may include the switch  306 , the resistor  310 , the voltage amplifier  312 , and the A/D converter  314 . 
     Referring now to  FIG. 4 , a flowchart depicts exemplary steps performed in analyzing the current signal from the current measurement module  316  of  FIG. 3 . Control begins in step  402 , where control determines whether the trigger signal has been activated. If so, control continues in step  404 ; otherwise, control remains in step  402 . In step  404 , a timer is started and control continues in step  406 . 
     In step  406 , control begins measuring current through the solenoid. Control continues in step  408 , where control begins calculating a moving average of the current. In order to prevent a false detection of a local maximum or local minimum, control may calculate a moving average of the current. In this way, small disturbances in the current signal, such as those due to noise, will not be incorrectly detected as a change in slope of the overall line. 
     For example only, the moving average may be a two-point moving average. The moving average may be calculated as a prior moving average or as a central moving average, which uses data taken after the point being calculated. In addition, the moving average may be a simple moving average or a weighted moving average, where the weighting may be linear or exponential. 
     Control continues in step  410 , where control begins calculating a derivative of the moving average. For example only, control may calculate the derivative as the difference between the current moving average value and the previous moving average value divided by the time between the moving average values. Control continues in step  412 , where control determines whether the derivative has decreased below 0. If so, control transfers to step  414 ; otherwise, control transfers to step  416 . For example only, control may transfer to step  414  only when multiple sequential derivatives remain below 0. 
     In step  416 , control determines whether the timer is greater than a predetermined maximum time. If so, control transfers to step  418 ; otherwise, control returns to step  412 . In step  414 , control determines whether the derivative has returned above 0 after being below 0 in step  412 . If so, control transfers to step  420 ; otherwise, control transfers to step  422 . As in step  412 , control may evaluate multiple derivatives in step  414  to ensure that the derivative has stably increased above 0. In step  422 , control determines whether the timer has exceeded the predetermined maximum time. If so, control transfers to step  418 ; otherwise, control returns to step  414 . In step  420 , control reports the timer value as the notch time and control stops. In step  418 , control reports the predetermined maximum time as the notch time and control stops. 
     Referring now to  FIG. 5A , a cross-sectional view of an exemplary implementation of the solenoid assembly  112  is shown. The solenoid assembly  112  includes the solenoid  300 . The solenoid  300  includes an armature  502 , a piston  504 , windings  506 , and a casing  508 . The casing  508  defines a chamber  510 . The armature  502  is held in the chamber  510  via a spring (not shown). 
     The solenoid  300  is inserted into a wall  520  of the oil sump  110 . The wall  520  is joined to a base  522  of the oil sump  110 . The seal between the solenoid  300  and the wall  520  may be maintained by an o-ring  524 . A drain plug  530  may be inserted into an opening of the wall  520 . The opening may be sealed against the drain plug  530  by an o-ring  526 . Oil in the oil sump  110  is indicated by shading, such as in spaces indicated by reference numerals  540  and  550 . The oil in the space  540  in the oil sump  110  is in fluid communication with the oil in the space  550 . The space  550  is open to the space  540 , although this connection is not visible in this cross-sectional view. 
     Levels of oil in the oil sump  110  may be defined. For example, a critical oil level  544  may be defined. If the level of oil in the oil sump  110  falls below the level  544 , the oil may be considered to be critically low. A low oil level  546  may also be defined. If the oil level is below the level  546  but above the level  544 , the oil level may be identified as low. A captive space  560  of oil may be defined by an enclosure  562 . The enclosure  562  may be cylindrical, making the captive space  560  a column. The enclosure  562  includes an opening at its bottom that connects to a horizontal channel  564 . The horizontal channel  564  is not open to the space  550  while the drain plug  530  is fully inserted. 
     The enclosure  562  also has an opening for the solenoid  300 . The solenoid  300  may include a sleeve  570  within which the piston  504  rides. The end of the sleeve  570  is inserted into the enclosure  562 , and may be sealed by an o-ring  572 . The sleeve may include one or more holes. For example only, the sleeve  570  is shown having two openings,  574 - 1  on top and  574 - 2  on bottom. 
     At the top of the enclosure  562  is an orifice  580 . When the oil level in the enclosure  562  is above the level  546 , oil will cover the orifice  580 . A second orifice  582  is opened axially through the armature  502  and the piston  504 . The second orifice  582  thereby fluidically couples the captive space  560  to the chamber  510 . If the oil level in the enclosure  562  is above the level  544 , the second orifice  582  will be submerged in oil. 
     A recess  584  is formed in the piston  504 . The recess  584  may wrap around the circumference of the piston  504 . The recess  584  is fluidically coupled to the second orifice  582  via an opening  586 . The opening  586  may be orthogonal to the second orifice  582 . 
     Referring now to  FIG. 5B , when the solenoid  300  is actuated, the armature  502  moves out of the chamber  510 . The piston  504  forces oil through the orifice  580  as well as the second orifice  582 . If the fluid immediately below the orifice  580  is air instead of oil, the viscosity seen by the solenoid  300  will be reduced. If air is present below the orifice  580 , the type of fluid (such as air or oil) above the orifice  580  may have an insignificant effect on the measured viscosity. If the oil level is below the level  544  when the solenoid  300  actuates, the second orifice  582  will be filled with air and the resistance seen by the solenoid  300  will be even lower still. 
     When both orifices  580  and  582  are submerged in oil, actuation of the solenoid  300  can be used to determine the viscosity of that oil. In order to obtain a representative sample of the oil in the oil sump  110 , the solenoid  300  may be left in the actuated position. In this way, the captive space  560  within the enclosure  562  is fluidically coupled to the remainder of the oil sump  110 , such as the spaces  540  and  550 . This fluidic coupling is accomplished through openings  574 - 1  and  574 - 2 , the opening  586 , the piston  504 , and the second orifice  582 . The solenoid  300  may be actuated repeatedly to agitate the oil and promote mixing of the oil. In addition, the solenoid  300  may act as a pump in pumping oil between the space  540  of the oil sump  110  and the captive space  560 . 
     When the drain plug  530  is removed, the oil in the oil sump  110 , including the space  540  and the captive space  560 , can be drained through the opening in the wall  520 . When the drain plug  530  is replaced, air is trapped within the captive space  560 . The small size of the orifice  580  and the surface tension of the oil may prevent oil from refilling the captive space  560  when the oil sump  110  is filled. 
     Therefore, after an oil change, the captive space  560  is filled with air while the remaining space  540  of the oil sump  110  is filled with oil. Actuating the solenoid  300  may therefore initially produce a low viscosity reading. However, if the solenoid  300  is actuated repeatedly, oil will fill the captive space  560 . The viscosity reading will then become that of the oil. An oil change event may therefore be detected by a normal viscosity prior to engine shutdown and a low viscosity upon engine startup that transitions to a normal viscosity once again. This and other scenarios are described in  FIGS. 6A-9B , and an exemplary summary of detected conditions is shown in  FIG. 11 . 
     Referring now to  FIG. 6A , a cross section graphically illustrates the solenoid  300  when the oil level is above the low oil level  546 . The solenoid  300  is therefore measuring viscosity of the oil.  FIG. 6B  shows exemplary historical traces of solenoid actuation. For example only, solenoid readings may be performed each time the vehicle is turned on. First and second traces  600  and  602  may correspond to two different vehicles and are plotted on a plane of notch delay versus time. The graphs shown in  FIGS. 6B ,  7 B,  8 B, and  9 B may encompass many engine key-on cycles. 
     The notch delay is the time from when the solenoid is commanded to actuate until the notch is measured. The notch time increases as viscosity of the oil increases. As shown in  FIG. 6B , trace  600  shows viscosity that slowly increases over time and then begins to increase more rapidly. This may be a sign of impending oil failure, and may be signaled as an error condition. Trace  602  shows a fairly flat trend in oil viscosity, although the oil viscosity is slowly decreasing. At a certain point, a low enough oil viscosity may no longer provide necessary lubrication for engine components, and an error condition may be signaled. 
     Referring now to  FIG. 7A , a cross section graphically illustrates a filling of the captive space  560  after an oil change. Because the drain plug  530  is replaced before oil is refilled, air is trapped within the captive space  560 . By actuating the solenoid  300  one or more times, the captive space  560  is filled with oil.  FIG. 7B  shows a historical chart of notch delay time. A sudden drop in notch delay time is seen at  604 . The notch delay time then quickly returns to the normal level. This may be an indication that an oil change event has occurred. 
     Referring now to  FIG. 8A , a cross section graphically illustrates when oil is below the low oil level. The oil is no longer present directly below the orifice  580 . Therefore, when the solenoid  300  is actuated, air is forced through the orifice  580  instead of oil, and the resulting viscosity measurement is lower. This lower level is shown in  FIG. 8B  at  610 .  FIG. 8B  also indicates that an oil change occurred at  612  after the engine oil had been low for a period of time. 
     Referring now to  FIG. 9A , a cross section graphically illustrates a critically low oil level. Because the oil is at a critically low level, the orifice  580  is exposed to air, and the second orifice  582  is no longer submerged in oil. This will result in a low viscosity being experienced by the solenoid  300 .  FIG. 9B  shows a period  620  of low oil followed by a period  622  of critically low oil. When the oil returns to a normal viscosity, it may be assumed that an oil change has been performed. 
     However, it is possible that the oil sump  110  has simply been filled. It may be possible to distinguish between these two scenarios by monitoring the rate at which, or the time during which, the measured viscosity increases. If the drain plug  530  had been removed, it would take longer for the captive space  560  to fill with oil. However, if the oil sump  110  has simply been filled with oil, the captive space  560  may already contain oil. This will lead to a faster increase in viscosity measurements as the solenoid  300  can quickly fill the remainder of the captive space  560 . 
     Referring now to  FIG. 10 , a graphical illustration of notch delay times over a number of solenoid cycles is presented. At cycle  1 , a fairly low solenoid response (or, notch delay time) is measured. Approximately the same time is measured at the second cycle. By the third cycle, the notch delay time has begun increasing. At cycle seven, the notch delay time approximately levels out for the remainder of the 12 cycles. This response may be characteristic of an oil change event. At cycle seven, the cylinder of oil is once again refilled and the solenoid response time will be a reflection of the viscosity of the oil. 
     Referring now to  FIG. 11 , a table depicts exemplary determinations made for various solenoid response measurements. In the first column, the solenoid measurement made at or before engine shutdown is shown. In the second column, the solenoid measurement made after engine startup is shown. This measurement may be made during engine startup or at some later time during operation of the vehicle. 
     The third column shows a solenoid measurement taken after the solenoid has been cycled multiple times. In the fourth column, the interpretations of the respective solenoid measurements are presented. The three solenoid measurements depicted in  FIG. 11  are low (L), medium (M), and high (H). A low measurement signifies a low level of oil in the captive space  560 . This corresponds to the orifice  580  and the second orifice  582  interfacing with air, which results in a low notch delay time. 
     A medium measurement corresponds to the second orifice  582  containing oil while the orifice  580  is exposed to air. This will produce a solenoid response higher than that of the low level. A high measurement corresponds to the orifices  580  and  582  both being submerged in oil. This will produce the highest notch delay time. This is detected as a normal oil level; the oil sump  110  may not be completely full, but the level is greater than the low oil level. 
     The condition where the orifice  580  is exposed to oil while the second orifice  582  is exposed to air may indicate an error condition. Although the top of the orifice  580  may be covered by oil, if the fluid below the orifice  580  is air, the air will be pressed through the orifice  580 , thereby determining the solenoid response. Therefore, in order to detect oil for the orifice  580  and air for the second orifice  582 , oil would need to be suspended below the orifice  580  while air was trapped in front of the piston  504 . This condition may be assumed to not occur in normal operation. 
     The first nine rows after the header in  FIG. 11  correspond to a low level of oil during the last engine shutdown. If engine oil is low upon startup and remains low, an oil critical signal may be produced. If the oil measurement is low at startup and transitions to medium, the oil is still low, but a partial fill event has been detected. 
     It is possible that an oil change has been performed. However, it is less likely because after an oil change the oil level should be high. If the response time is low and transitions to high, a fill event is detected. Again, an oil change may have been performed. As described above, the amount of time consumed in transitioning from a low response to a high response may determine whether the oil has been changed or simply filled. 
     If the response at startup is medium and transitions to low, the oil critical signal may be generated. However, this may be an unexpected scenario. For the remaining rows where the response was low at shutdown, an unexpected event may be detected. Because the response was low at shutdown and the captive space  560  should remain closed off from additional oil, detection of a medium or high response upon startup may be anomalous. 
     The next nine rows correspond to a medium response prior to engine shutdown. If, upon startup, the response is low, it may be inferred that the drain plug  530  was removed. If the solenoid response does not transition away from low, however, the oil level is still critical. In this case, the oil may have been drained without adding additional oil. 
     If the solenoid response transitions from low to medium, an oil change event is apparent. However, the oil was not fully refilled. This may also indicate an unexpected scenario. If the solenoid response transitions to high, a normal oil change event is detected. If, upon startup, the response is medium and transitions to low, this could be the result of normal oil loss. The oil level is now critical. 
     If the response stays at medium, the oil level is low. If the solenoid response transitions to high, the oil sump  110  may have been filled to correct the low oil condition. If the response upon startup is high when the response prior to shutdown is medium, this may represent an unexpected event. 
     The final set of nine rows corresponds to a high response prior to engine shutdown. At startup, if the response is low and remains low, it appears that the oil has been drained. If the response transitions from low to medium, an oil change event has occurred. However, the oil has not been completely refilled. If the response transitions from low to high, a normal oil change event is detected. If the response upon startup is medium and the response at shutdown was high, this may represent an unexpected event. A leak may have occurred somewhere within the solenoid assembly  112 , for example. 
     If the response begins at high and transitions to low, the oil level is critical. Similarly, if the response transitions to medium, the oil level is low. If the response remains at high, the oil level appears to be acceptable and no events have been detected. In each of the cases where the response after cycling is high, oil viscosity may be measured. 
     Referring now to  FIG. 12 , a functional block diagram of an exemplary implementation of the oil diagnosis module  106  is presented. The oil diagnosis module  106  may include the current measurement module  316 . The current measurement module  316  provides measurements of current flowing through the solenoid  300  to a notch detection module  702 . 
     A voltage measurement module  704  may measure the voltage being output by the voltage supply  302 . The voltage measurement module  704  provides this voltage information to the notch detection module  702 . The solenoid control module  304  may control the solenoid  300  or may actuate a switch, which selectively allows current to flow through the solenoid  300 . For example only, the switch may be located within the current measurement module  316 . 
     A trigger signal from the solenoid control module  304  activates the switch within the current measurement module  316 , thereby actuating the solenoid  300 . The trigger signal is also received by the notch detection module  702 . Upon receiving the trigger signal, the notch detection module  702  may initialize a timer in a timer module  706 . The notch detection module  702  determines the delay time of the current notch, as described in  FIGS. 2-4 . The notch delay time is provided to a notch analysis module  710 . 
     The notch analysis module  710  may instruct the solenoid control module  304  to actuate the solenoid  300  one or more times. The notch analysis module  710  may store calibration data in a storage module  712 . For example, the calibration data may indicate what ranges of notch delay times fall within response categories, such as high, medium, and low. The notch analysis module  710  may receive control signals from the engine control module  104 , and may provide oil viscosity level, oil level, and oil change event information to the engine control module  104 . 
     Because oil viscosity may increase as oil temperature increases, the notch analysis module  710  may normalize the oil viscosity level to a reference oil temperature. For example only, the oil temperature may be measured directly, modeled, and/or inferred from other temperature measurements, such as engine coolant temperature. In various implementations, viscosity values may be stored in a lookup table indexed by oil temperature and notch delay time. The values in the lookup table may be determined empirically or estimated based on solenoid characteristics, such as orifice and piston geometries. 
     The notch detection module  702  may use voltage information from the voltage measurement module  704  to scale values from the current measurement module  316 . In addition, the notch delay time may be adjusted based upon the voltage. For example only, a higher voltage from the voltage supply  302  may decrease the notch delay time. The notch detection module  702  may therefore increase the indicated notch delay time when the voltage is higher. 
     Referring now to  FIG. 13 , a flowchart depicts exemplary operation of the notch analysis module  710  of  FIG. 12 . Control begins in step  802 , where the solenoid is cycled. Control continues in step  804 , where the notch time is determined. Control continues in step  806 , where the notch time is stored. Control continues in step  808 , where the solenoid is cycled a predetermined number of times. For example, the solenoid may be cycled enough times to fill the volume of the captive space  560  with oil from the remaining portion of the oil sump  110 . 
     Control continues in step  810 , where the solenoid is cycled one or more times. Control continues in step  812 , where the notch time is determined. Control continues in step  814 , where control determines whether there is a change in notch time from the previous measurement. If so, control returns to step  810  to continue cycling the solenoid until the notch time stabilizes. Otherwise, control transfers to step  816 . In step  816 , the notch time is stored. 
     Control continues is step  818 , where the stored notch times are evaluated. The stored notch times include the notch times stored after the first cycle in step  806 , as well as the notch time stored in step  816  after the notch time stabilized. The stored notch times may also include notch times stored from previous engine runs, such as the last notch time determined before the engine shut down. This evaluation may be performed using a table, such as that depicted in  FIG. 11 . Control continues in step  820 , where the results are reported. Control then stops. 
     The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, 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.