Diagnostic method for a shaft sensor in a reciprocating internal combustion engine

Information

  • Patent Grant
  • 6640621
  • Patent Number
    6,640,621
  • Date Filed
    Thursday, March 29, 2001
    23 years ago
  • Date Issued
    Tuesday, November 4, 2003
    21 years ago
Abstract
An improved method of diagnosing shaft sensor failure in a reciprocating internal combustion engine verifies engine rotation by sensor information responsive to dynamic variation in engine air intake that occurs during engine rotation. Failure of the shaft sensor is diagnosed when the dynamic variation in engine air intake is detected in the absence of a shaft sensor signal. The sensor information used to detect the dynamic variation in intake air may be obtained from either a mass air flow sensor disposed in a throttle passage of the engine, or from a pressure sensor disposed in an intake manifold of the engine, and virtually all current engine control systems utilize at least one of these sensors. The dynamic variation is detected by recognizing rising and falling segments of the signal waveform, by comparing the relative manifold pressure to predetermined maximum and minimum values, or by using a derivative of the signal waveform to recognize its inflection points.
Description




TECHNICAL FIELD




This invention relates to shaft motion sensing in a reciprocating internal combustion engine, and more particularly to a method of diagnosing proper operation of a shaft sensor.




BACKGROUND OF THE INVENTION




Control systems for reciprocating internal combustion engines rely extensively on input signals obtained from various types of sensors. One of the most important inputs is obtained from a sensor (usually a magnetic flux responsive sensor) positioned in proximity to the teeth of a rotary wheel such the engine flywheel gear for providing an indication of crankshaft movement; typically, this input is used by the engine controller to determine both engine crankshaft position (rotary orientation) and speed for purposes of properly regulating control parameters such as spark timing and fuel delivery. Accordingly, it is highly desirable to promptly diagnose crankshaft sensor failures so that alternate or default control strategies may be initiated. Since the use of redundant sensors is usually cost prohibitive, failure of the crankshaft sensor is sometimes diagnosed on the basis of an input provided by a camshaft sensor, as the camshaft is mechanically coupled to the crankshaft. However, not all engine control systems include a camshaft sensor. Accordingly, what is desired is a method of diagnosing crankshaft sensor failures based on sensor information that is routinely available in an engine control system.




SUMMARY OF THE INVENTION




The present invention is directed to an improved method of diagnosing shaft sensor failure in a reciprocating internal combustion engine in which engine rotation is verified by sensor information responsive to dynamic variation in engine air intake that occurs during engine rotation, and failure of the shaft sensor is diagnosed when the dynamic variation in engine air intake is detected in the absence of a shaft sensor signal. The sensor information used to detect the dynamic variation in intake air may be obtained from either a mass air flow sensor disposed in a throttle body of the engine, or from a pressure sensor disposed in an intake manifold of the engine, and virtually all current engine control systems utilize at least one of these sensors. Three different methodologies for detecting dynamic variation of the air intake signal are described. According to a first embodiment, the variation is detected by recognizing rising and falling segments of the signal waveform. In a second embodiment, the variation is detected by computing a relative manifold pressure and comparing it to predetermined maximum and minimum values. In a third embodiment, the variation is recognized by using a derivative of the signal to recognize the waveform inflection points.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic diagram of selected components of an engine control system according to this invention, including an intake manifold absolute pressure sensor and a microprocessor-based engine control module.





FIG. 2

is a graph depicting typical fluctuations of intake manifold absolute pressure in a four-cylinder gasoline engine as a function of time.





FIG. 3

is a graph depicting one cycle of the waveform of

FIG. 2

, marked to identify waveform segments used to recognize fluctuation according to a first embodiment of this invention.





FIG. 4

, Graphs A, B and C, illustrates the waveform of FIG.


2


and transition timing signals developed according to the first embodiment.





FIG. 5

is a graph depicting one cycle of a relative MAP signal, along with maximum and minimum thresholds according to a second embodiment of this invention.





FIG. 6

, Graphs A, B and C, illustrates an extended version of the waveform of FIG.


2


and transition timing signals developed according to the second embodiment.





FIG. 7

is a graph depicting one cycle of the waveform of

FIG. 2

, along with data segments relating to a first derivative to recognize fluctuation according to a third embodiment of this invention.





FIG. 8

, Graphs A, B and C, illustrates the waveform of FIG.


2


and transition timing signals developed according to a third embodiment of this invention.





FIG. 9

is a flowchart representing a software routine executed by the engine control module of

FIG. 1

in carrying out the first embodiment of this invention.





FIG. 10

is a flowchart representing a software routine executed by the engine control module of

FIG. 1

in carrying out the second embodiment of this invention.





FIG. 11

is a flowchart representing a software routine executed by the engine control module of

FIG. 1

in carrying out the third embodiment of this invention.











DESCRIPTION OF THE PREFERRED EMBODIMENT




The present invention is disclosed in the context of an engine control system including a four-cylinder gasoline engine generally designated in

FIG. 1

by the reference numeral


10


. Referring to

FIG. 1

, the engine


10


includes four pistons


12


(only one of which is shown) which reciprocate in respective cylinders


14


and are connected to crankshaft


16


. The crankshaft


16


is connected to the crank-wheel


18


, which is mechanically coupled to a cam-wheel


20


by a belt or chain


21


so that the crank-wheel


18


and the cam-wheel


20


rotate synchronously. The cam-wheel


20


is connected to a camshaft


22


, which opens and closes a cylinder intake valve


24


through a mechanical linkage


25


in coordination with the movement of piston


12


. Intake air enters an intake manifold


26


through a throttle passage


27


, and is delivered to each of the cylinders


14


via a respective intake runner


28


and intake valve


24


. Obviously, engine


10


includes many other component parts that are also conventional and known in the state of the art to be part of an operational engine system.




The operation of engine


10


is regulated by a microprocessor-based engine control module (ECM)


29


in response to a number of inputs, including a crankshaft position signal developed by a sensor


30


responsive to movement of crank-wheel


18


, and a manifold absolute pressure (MAP) signal developed by a pressure sensor


34


responsive to the air pressure in intake manifold


26


. Optionally, a sensor


32


may be provided as shown to detect movement of the cam-wheel


20


. In some systems, a mass air-flow (MAF) sensor


36


is utilized to measure the intake air-flow in throttle passage


27


; most systems use either a MAP sensor or a MAF sensor, but some systems use both. As indicated above, the present invention is directed to a method of diagnosing a failure of sensor


30


based on an analysis of signals responsive to dynamic variation in engine air intake that occurs during engine rotation; such a signal may be provided by either MAP sensor


34


or MAF sensor


27


. In the ensuing description, however, a diagnostic method based on the MAP signal is described.




Referring to

FIG. 2

, the trace


102


depicts a typical variation in the MAP signal with respect to time during rotation (crank or run) of the four-cylinder engine


10


. The variation occurs due to the reciprocation of pistons


12


within the respective cylinders


14


. When a respective intake valve


24


is opened and the piston


12


moves downward as viewed in

FIG. 1

, the cylinder volume is enlarged, and air is drawn into the cylinder


14


from intake manifold


26


, reducing the MAP signal. The reduction in pressure causes ambient air to enter intake manifold


26


through throttle passage


27


, restoring the pressure in intake manifold


26


. This process occurs repetitively for each of the cylinders


14


, resulting in the periodic MAP signal fluctuation depicted by the trace


102


. It will be recognized, of course, that the MAF signal is subject to a very similar fluctuation.




According to this invention, ECM


29


detects the signal fluctuation due to the aforementioned dynamic variation in intake air during engine rotation, and diagnoses a failure of the sensor


30


when the dynamic variation is detected in the absence of a crankshaft position signal. Three different methodologies for detecting the MAP signal fluctuation are described below. In the first methodology, described in reference to

FIGS. 3-4

and the flow chart of

FIG. 9

, the signal fluctuation is detected by recognizing rising and falling segments of the MAP waveform. In the second methodology, described in reference to

FIGS. 5-6

and the flow chart of

FIG. 10

, the signal fluctuation is detected by comparing the relative manifold pressure to predetermined maximum and minimum values. In the third methodology, described in reference to

FIGS. 7-8

and the flow chart of

FIG. 11

, the signal fluctuation is detected by computing a derivative of the MAP waveform to recognize its inflection points. Once a predetermined number of MAP cycles have been identified, the engine crankshaft


16


is deemed to be turning, and a failure of the sensor


30


is diagnosed if a crankshaft position signal is not present.




Referring to

FIGS. 3-4

, rising and falling segments of the MAP waveform characteristic of engine rotation are identified by recognizing successive pressure rises Pr and pressure drops Pd per unit time (that is, positive and negative slopes) in excess of respective predetermined thresholds.

FIG. 3

depicts a representative cycle of the waveform, along with a detected pressure rise Pr and pressure drop Pd in the respective time intervals t−1 to t and t+n−1 to t+n. An extended segment of the same waveform is depicted in Graph A of

FIG. 4

, showing several identified rising segments


306


,


310


,


314


and


318


and several identified falling segments


304


,


308


,


312


and


316


. Graphs B and C depict Flags used to identify the rising and falling segments. The Enable Flag, depicted in Graph B, is briefly set to indicate that a rising segment has been identified, and the Transition Complete Flag, depicted in Graph C, changes state at each rising and falling segment identification. At such point as rising segments


306


,


310


,


314


and


318


are identified and the Transition Complete Flag is set, the Enable Flag is set to indicate that this identification has been made, and the Transition Complete Flag is reset, as can be seen at times t


2


, t


4


, t


6


and t


8


. At such point as falling segments


304


,


308


,


312


and


316


are identified and the Transition Complete Flag is not set, the Transition Complete Flag is set to indicate that this identification has been made, as can be seen at time t


1


, t


3


, t


5


and t


7


.




A software routine periodically executed by ECM


29


for carrying out this methodology is depicted in

FIG. 9

, where blocks


320


and


322


are first executed to calculate the change in MAP from the value stored during the previous execution of the routine, and to store the current value of MAP for use in the next execution of the routine. If the Transition Complete Flag is false, as determined at block


324


, the block


326


sets the Enable Flag to False, and the block


328


checks for a falling MAP waveform segment by comparing the computed change in MAP to a negative threshold (Calibration 1). As soon as a falling segment is identified, the block


330


sets the Transition Complete Flag to True so that in the next execution of the routine, the block


332


will be executed to check for a rising segment. Checking for a rising MAP waveform segment involves comparing the computed change in MAP to a positive threshold (Calibration 2), as indicated at block


332


. If the change in MAP is greater than Calibration 2, a rising segment is identified, and the blocks


334


,


336


and


338


are executed to set the Transition Complete Flag to false, to set the Enable Flag to true, and to increment a count of the number of cycles in which conditions have been correct to set the Enable Flag. If the count exceeds a threshold (Calibration 3), as determined at block


340


, the crankshaft is deemed to be rotating, and block


342


checks if the crankshaft signal is present. If so, the routine is exited; if not, the block


344


sets the Crankshaft Sensor Malfunction Flag to True.




In FIG.


5


and Graph A of

FIG. 6

, the traces


402


and


502


respectively depict the relative manifold pressure—that is, the difference between MAP and the ambient barometric pressure BARO (which is also a measured quantity) as a function of time. In this embodiment, the relative manifold pressure is compared to predetermined maximum and minimum thresholds identified by the traces


406


and


410


, respectively. In the extended waveform segment of Graph A of

FIG. 6

, crossings of the maximum threshold


406


are identified by the reference numerals


506


,


510


,


514


and


518


and crossings of the minimum threshold


410


are identified by the reference numerals


504


,


508


,


512


and


516


. As in

FIG. 4

, Graph B depicts the Enable Flag, and Graph C depicts the Transition Complete Flag. At such points as the waveform exceeds the maximum threshold


408


(points


506


,


510


,


514


and


518


) and the Transition Complete Flag is set, the Enable Flag is set to indicate that this identification has been made and the Transition Complete Flag is reset as can be seen at time t


2


, t


4


, t


6


and t


8


. At such point as the waveform falls below the minimum threshold


410


(points


504


,


508


,


512


and


516


) and the Transition Complete Flag is not set, the Transition Complete Flag is set to indicate that this identification has been made as can be seen at time t


1


, t


3


, t


5


and t


7


.




A software routine periodically executed by ECM


29


for carrying out this methodology is depicted by the flow chart of

FIG. 10

, where block


520


is first executed to calculate the relative MAP according to the difference (MAP—BARO). If the Transition Complete Flag is false, as determined at block


524


, the block


526


sets the Enable Flag to False, and the block


528


compares relative MAP to a negative threshold (Calibration 1). When relative MAP falls below Calibration 1, the block


530


sets the Transition Complete Flag to True so that in the next execution of the routine, the block


532


will be executed to check for a positive-going fluctuation. The block


532


compares the relative MAP to a positive threshold (Calibration 2), and if the relative MAP exceeds Calibration 2, the blocks


534


,


536


and


538


are executed to set the Transition Complete Flag to false, to set the Enable Flag to true, and to increment a count of the number of cycles in which conditions have been correct to set the Enable Flag. If the count exceeds a threshold (Calibration 3), as determined at block


540


, the crankshaft is deemed to be rotating, and block


542


checks if the crankshaft signal is present. If so, the routine is exited; if not, the block


544


sets the Crankshaft Sensor Malfunction Flag to True.




Referring to

FIGS. 7-8

, rising and falling segments of the MAP waveform characteristic of engine rotation are identified by using a derivative of the waveform to identify inflection points. In

FIG. 7

, the MAP waveform


102


may be sampled over several periods of time, specifically from time t−1 to t, from time t to t+1, from time t+n−1 to t+n and from time t+n to t+n+1. The difference of MAP change (pressure rise P


r1


, P


r2


and pressure drop P


d1


, P


d2


) for each time period is calculated, along with the difference of two adjacent segments, so as to compute the mathematical derivative of the waveform. Thus the difference Pr


1


−Pr


2


gives the derivative of the waveform at time t, and the difference Pd


1


−Pd


2


gives the derivative at time t+n. When the derivative is very close to zero, an inflection point is recognized (i.e, the waveform changes from convex-to-concave or concave-to-convex), and it is expected that there will be only two inflection points during each cycle. Of course, a second or higher derivative of MAP waveform may be used since the waveform


102


closely approximates a sine wave and all degrees of derivative have the same shape but are shifted in time. An extended segment of the same waveform is depicted in Graph A of

FIG. 8

, showing several identified concave-to-convex inflection points


706


,


710


,


714


and


718


and several convex-to-concave inflection points


704


,


708


,


712


and


716


. As in

FIGS. 4 and 6

, Graph B depicts the Enable Flag, and Graph C depicts the Transition Complete Flag. At such points as a rising inflection is identified (points


706


,


710


,


714


and


718


) and the Transition Complete Flag is set, the Enable Flag is set to indicate that this identification has been made and the Transition Complete Flag is reset as can be seen at time t


2


, t


4


, t


6


and t


8


At such points as a falling inflection is identified (points


704


,


708


,


712


and


716


) and the Transition Complete Flag is not set, the Transition Complete Flag is set to indicate that this identification has been made as can be seen at time t


1


, t


3


, t


5


and t


7


.




A software routine periodically executed by ECM


29


for carrying out this methodology is depicted in

FIG. 11

, where blocks


720


,


722


,


724


and


726


are first executed to calculate the change in MAP from the MAP value stored during the previous execution of the routine, to calculate the MAP derivative from the change in MAP values, and to store the current change in MAP and the current value of MAP for use in the next execution of the routine. If the Transition Complete Flag is false, as determined at block


728


, the block


730


sets the Enable Flag to False, and the block


732


checks for a negative inflection point. If the computed MAP derivative is substantially zero and the change in MAP is negative, a negative inflection point is identified, and the block


734


sets the Transition Complete Flag to True so that in the next execution of the routine, the block


736


will be executed to check for a positive inflection point. Block


736


identifies a positive inflection point when the computed MAP derivative is substantially zero and the change in MAP is positive; in such case, the blocks


738


,


740


and


742


are executed to set the Transition Complete Flag to false, to set the Enable Flag to true, and to increment a count of the number of cycles in which conditions have been correct to set the Enable Flag. If the count exceeds a threshold (Calibration 3), as determined at block


744


, the crankshaft is deemed to be rotating, and block


746


checks if the crankshaft signal is present. If so, the routine is exited; if not, the block


748


sets the Crankshaft Sensor Malfunction Flag to True.




In summary, the above-described method provides a simple and cost-effective way of diagnosing failure of an engine shaft sensor such as the crankshaft sensor


30


based on sensor information responsive to dynamic variation in engine air intake that occurs during engine rotation. While the present invention has been described in reference to the illustrated embodiments, it is expected that various modifications in addition to those mentioned above will occur to those skilled in the art. For example, engine


10


may be two-stroke engine instead of a four-stroke engine, or may have fewer than or more than four cylinders. Accordingly, it will be understood that methods incorporating these and other modifications may fall within the scope of this invention, which is defined by the appended claims.



Claims
  • 1. A diagnostic method for a reciprocating internal combustion engine system having a shaft sensor responsive to an engine shaft for producing a shaft signal indicative of movement of said engine shaft, the method comprising the steps of:producing an air intake signal responsive to air intake of said engine; analyzing said air intake signal to detect a dynamic variation in the air intake that is characteristic of engine rotation; and diagnosing a failure of said shaft sensor when said dynamic variation is detected but said shaft signal indicates that said shaft is not moving.
  • 2. The diagnostic method of claim 1, wherein said air intake signal is produced by sensing mass airflow in a throttle passage of said engine.
  • 3. The diagnostic method of claim 1, wherein said air intake signal is produced by sensing a pressure in an intake manifold of said engine.
  • 4. The diagnostic method of claim 3, where the step of analyzing said air intake signal includes the steps of:measuring an ambient air pressure; computing a relative air pressure signal based on a difference between said air intake signal and the measured ambient air pressure; comparing said relative air pressure signal to upper and lower thresholds to identify successive excursions of said relative air pressure signal above said upper threshold and below said lower threshold; and detecting a dynamic variation in said air intake when a predetermined number of said successive excursions have been identified.
  • 5. The diagnostic method of claim 1, where the step of analyzing said air intake signal includes the steps of:detecting increases and decreases of said air intake signal over given intervals of time; identifying successive detected increases of said air intake signal in excess of a first threshold and detected decreases of said air intake signal in excess of a second threshold; and detecting a dynamic variation in said air intake when a predetermined number of said successive detected increases and decreases have been identified.
  • 6. The diagnostic method of claim 1, where the step of analyzing said air intake signal includes the steps of:determining a derivative of said air intake signal; using the determined derivative to identify successive positive and negative inflections of said air intake signal; and detecting a dynamic variation in said air intake when a predetermined number of said successive positive and negative inflections have been identified.
  • 7. The diagnostic method of claim 6, including the steps of:computing changes in said air intake signal over a number of successive time intervals; determining the derivative of said air intake signal based on a change in successively computed changes; detecting a positive inflection of said air intake signal when said derivative is substantially zero and the computed change in the air intake signal is positive; detecting a negative inflection of said air intake signal when said derivative is substantially zero and the computed change in the air intake signal is negative.
Parent Case Info

This application claims priority to U.S. Provisional Application No. 60/208,236 filed May 31, 2000.

US Referenced Citations (3)
Number Name Date Kind
4402217 Higashiyama Sep 1983 A
5824890 Le Palm et al. Oct 1998 A
6425362 Kanno Jul 2002 B1
Provisional Applications (1)
Number Date Country
60/208236 May 2000 US