Abstract:
A method for determining the position of a crankshaft without the use of a signal from a dedicated crankshaft position sensor. The method includes the steps of providing a pulse sensor for generating a signal in response to the transmission of vibrations through the engine block; evaluating the signal generated by the pulse sensor to identify a series of combustion events, the series of combustion events being made up of a series of individual combustion events occurring in the plurality of cylinders, the individual combustion events taking place in a predetermined order; and evaluating the series of combustion events to identify a reference crankshaft position by correlating at least one of the individual combustion events to an associated one of the plurality of cylinders.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates generally to an internal combustion engines and more particularly to a method of replicating a crankshaft position signal for an internal combustion engine.  
           [0003]    2. Discussion  
           [0004]    Modern internal combustion engines include a crankshaft that is mechanically linked to a camshaft. The relative positions of the crankshaft and camshaft are obtained through sensing mechanisms, such as a dedicated crankshaft position sensor and a camshaft position sensor, respectively. The signal from these sensors is transmitted to a mechanism, such as an engine controller, for controlling engine functions, such as spark and fuel timing. For example, the engine controller utilizes the signal from the crankshaft position sensor to control operations dependant upon crankshaft position, such as the timing of the spark and the dispensing of fuel through the fuel injectors. Similarly, the engine controller utilizes the signal from the dedicated camshaft position sensor to establish the rotational position of the crankshaft relative to the camshaft (i.e., synchronize the crankshaft to the camshaft). As most modern engines are of the four-cycle design, the crankshaft rotates two complete revolutions to every one revolution of the camshaft. Synchronization of the crankshaft to the camshaft prevents the engine controller from dispensing fuel and firing a spark when the camshaft is 180 degrees out of position.  
           [0005]    If for any reason the signal from the dedicated crankshaft position sensor were unavailable, the engine controller would not be able to control the engine operations that are dependant upon the crankshaft position, thus preventing the engine from operating. Thus, there is a need in the art for a method of determining the absolute position of a crankshaft in the absence of a crankshaft position signal from a dedicated crankshaft position sensor.  
         SUMMARY OF THE INVENTION  
         [0006]    It is one object of the present invention to provide a method for determining the position of a crankshaft without the use of a signal from a dedicated crankshaft position sensor. The method includes the steps of providing a pulse sensor for generating a signal in response to the transmission of vibrations through the engine block; evaluating the signal generated by the pulse sensor to identify a series of combustion events, the series of combustion events being made up of a series of individual combustion events occurring in the plurality of cylinders, the individual combustion events taking place in a predetermined order; and evaluating the series of combustion events to identify a reference crankshaft position by correlating at least one of the individual combustion events to an associated one of the plurality of cylinders.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings wherein:  
         [0008]    [0008]FIG. 1 is a schematic diagram of an engine control system constructed and operated in accordance with the teachings of the present invention;  
         [0009]    [0009]FIG. 2A is a schematic diagram of an exemplary crankshaft position signal;  
         [0010]    [0010]FIG. 2B is a schematic diagram of an exemplary camshaft position signal;  
         [0011]    [0011]FIG. 2C is a schematic diagram of an exemplary pulse signal illustrating a series of combustion events;  
         [0012]    [0012]FIG. 3 is a schematic diagram in flowchart form of the method for determining the position of a crankshaft according to a preferred embodiment of the present invention; and  
         [0013]    [0013]FIG. 4 is a schematic diagram in flowchart form of the method for determining the position of a crankshaft according to an alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    Referring to FIG. 1, an engine control system  10  used in conjunction with a method according to a first embodiment of the present invention is schematically illustrated with a four-cycle internal combustion engine  12 . Engine  12  includes an engine block  13  that is partially shown in a cut-away view, illustrating one of a plurality of cylinders  14  in engine  12 . In the particular example provided, engine  12  includes four cylinders  14 . Engine  12  includes a piston  16  disposed within each cylinder  14  which is operably connected by a connecting rod  18  to a crankshaft  20 . A camshaft  22  is used to open and close at least one intake valve (not shown) and at least one exhaust valve (not shown) of cylinder  14  for various strokes of piston  16 . In a four-stroke spark-ignited engine, these strokes include intake, compression, power and exhaust. It should be appreciated that crankshaft  20  and camshaft  22  are mechanically linked together.  
         [0015]    Engine control system  10  includes a crankshaft sensor target  24 , a camshaft sensor target  26 , a crankshaft position sensor  28 , a camshaft position sensor  29 , a pressure pulse sensor  30  and an engine controller  32 . Crankshaft sensor target  24  is coupled for rotation with crankshaft  20  and has at least one, but preferably a plurality of trip points  34  that are employed by crankshaft position sensor  28  to generate a crankshaft position signal. With additional reference to FIG. 2A, crankshaft sensor target  24  includes four trip points  34  and as such, crankshaft position sensor  28  produces a crankshaft position signal  40  having four peaks  42  per revolution of the crankshaft  20  in the particular example provided.  
         [0016]    Similarly, camshaft sensor target  26  is coupled for rotation with the camshaft  22  and preferably includes a single trip point  36  that is employed by the camshaft position sensor  29  to generate a camshaft position signal. With additional reference to FIG. 2B, the camshaft position sensor  29  produces a camshaft position signal  48  having one peak  50  per two revolutions of the crankshaft  20  since the camshaft  22  rotates at one-half the velocity of the crankshaft  20 .  
         [0017]    The pressure pulse sensor  30  is mounted to engine  12  to either directly monitor cylinder pressure or to indirectly monitor the effects of the pressure pulse on another fluid, such as air, oil or coolant. It should be noted, however, that as most modern vehicles already include at least one knock or detonation sensor  52  which generates a signal in response to the transmission of vibrations through the engine block  13 , the use of an accelerometer or detonation sensor for detecting pressure pulses is preferred so as to eliminate the need to incorporate additional sensors into engine  12 . A detonation sensor  52  is also preferred due to its typical sensitivity and rate of response. With additional reference to FIG. 2C, the pressure pulse sensor  30  produces a pressure pulse signal  54  having four peaks  58  per two revolutions of the crankshaft  20 , with each peak corresponding to a combustion event in one of the plurality of engine cylinders  14 .  
         [0018]    The engine controller  32  includes a time keeping mechanism or timer  64  and is coupled to the crankshaft position sensor  28 , the camshaft position sensor  29  and the pulse sensor  30  and receives their output. Those skilled in the art will understand that the engine  12  also includes various other sensors (e.g., a throttle position sensor and a manifold absolute pressure sensor) and hardware to permit the engine  12  to carry out its operation which are not shown but conventional and well known in the art. The outputs of these sensors also communicate with engine controller  32 .  
         [0019]    It should be appreciated that engine controller  32  utilizes the outputs of sensors  28  and  29  to determine the radial position of the crankshaft  20  and thereby determine the position of piston  16  within cylinder  14 . It should further be appreciated that the output from crankshaft position sensor  28  is used to determine a speed of engine  12 , typically measured in revolutions per minute (RPM), as well as to control a plurality of crankshaft position dependent operations. One crankshaft position dependent operation is the spark timing or spark advance. The spark timing is the timing of the delivery of a spark to a cylinder  14  and is typically quantified as the number of crankshaft angle degrees before top-dead-center on the compression stroke. The engine controller  32  controls the spark timing to initiate a spark (via a spark plug which is not shown) in an individual cylinder to burn a charge of fuel in that cylinder. Other crankshaft position dependent operations may include, for example, the timing of the delivery of fuel to an individual cylinder and the actuation of a mechanism, such as a decompression valve, to decompress an individual cylinder for engine braking.  
         [0020]    It should be appreciated that detonation sensor  52  detects vibration within engine  12  and that the engine controller  32  utilizes the output signal of the detonation sensor  52  to identify peaks  58  in the pressure pulse signal  54 . Detonation sensor  52  is operable for measuring low intensity vibrations caused by combustion events in the individual cylinders  14  which are created when crankshaft  20  is rotated and fuel in the individual cylinders  14  is combusted. Preferably, each combustion event produces a peak  58  in the pressure pulse signal  54  that can be correlated to the individual cylinder  14  in which the combustion event occurred. Operation in this manner provides increased accuracy and reduces the time that is necessary to determine the position of the crankshaft  20 . With specific reference to FIG. 2C, each of the peaks  58  in the pressure pulse signal  54  is indicative of a combustion event in an associated one of the cylinders  14 . In the particular example provided, the detonation sensor  52  is located closest to a cylinder  14  identified as “cylinder  1 ” and is progressively further from those cylinders  14  identified as “cylinder  2 ”, “cylinder  3 ” and “cylinder  4 ”. Since the magnitude of the vibrations produced by combustion events in each of the cylinders  14  varies with the distance between the detonation sensor  52  and the particular cylinder  14  in which the combustion event occurred, and since the firing order of the engine  12  is known, correlation of a combustion event to a particular cylinder  14  when the engine  12  is operating under relatively steady conditions can be accomplished relatively quickly and accurately.  
         [0021]    In this regard, a series of combustion events  70  is first identified, with the series of combustion events  70  including one combustion event in each of the individual cylinders  14 . As mentioned above, each combustion event is identified by a peak  58 . Once a series of combustion events  70  has been identified, the position of the crankshaft  20  can be determined by correlating one or more of the  20  peaks  58  to a particular cylinder  14 . In the example provided, the peak  58   a  is of the highest magnitude and as such, must correlate to cylinder  1  since cylinder  1  is closest to the detonation sensor  52 . Similarly, peaks  58   b ,  58   c  and  58   d  decrease in magnitude and as such, correlate to cylinders  2 ,  3  and  4 , respectively, since these cylinders are increasingly further from the detonation sensor  52 . Those skilled in the art will understand that correlation between the peaks  58  and the individual cylinders  14  may alternatively be accomplished through the use of look-up tables that permit peak  58  to be associated directly with an individual cylinder  14  based on its absolute magnitude and the current operating conditions (e.g., manifold absolute pressure and rotational speed).  
         [0022]    Referring to FIG. 3, a method for determining the position of a crankshaft  20  according to the teachings of the present invention is schematically illustrated in flowchart form. The methodology begins at bubble  100  and progresses to block  104  wherein the methodology utilizes the camshaft position signal  48  and the crankshaft position signal  40  to determine the position of the crankshaft  20 . The methodology proceeds to decision block  108  and determines whether the crankshaft sensor  28  has failed.  
         [0023]    If the crankshaft sensor  28  has not failed, the methodology loops back to block  104 . If the crankshaft sensor  28  has failed in decision block  108 , the methodology proceeds to block  112  where the pressure pulse signal  54  is evaluated to identify a series of combustion events  70 . Those skilled in the art will understand that filtering of the signal produced by the detonation sensor  52  may be needed to permit each of the peaks  58  to be identified. The methodology next proceeds to block  116  wherein the series of combustion events  70  is employed to identify a crankshaft reference position by correlating at least one of the combustion events to an individual cylinder  14 .  
         [0024]    The methodology next proceeds to block  120  where the methodology calculates the rotational velocity of the crankshaft  20  and employs the crankshaft reference position and the series of combustion events  70  to control a plurality of crankshaft dependent operations. The method then loops back to decision block  108 .  
         [0025]    A method according to the teachings of an alternate embodiment of the present invention is illustrated in FIG. 4. The method begins at bubble  200  and progresses to block  204  where the methodology utilizes the camshaft position signal  48  and the crankshaft position signal  40  to determine an actual camshaft position and an actual crankshaft position. The methodology then proceeds to block  208  where the pressure pulse signal  54  is evaluated to identify a series of combustion events  70 . The methodology next proceeds to block  212  wherein the series of combustion events  70  and the actual camshaft position are employed to identify a crankshaft reference position. The methodology then proceeds to block  216  where the methodology employs the crankshaft reference position to determine a reference camshaft position. The methodology next process to decision block  220 .  
         [0026]    In decision block  220 , the methodology compares the actual camshaft position to the reference camshaft position and determines if they vary from one another by more than a first predetermined amount. If the actual camshaft position and the reference camshaft position vary by more than the first predetermined amount, the methodology proceeds to block  224  wherein a first fault code is generated. The methodology then proceeds to decision block  228 . Returning to decision block  220 , if the actual camshaft position and the reference camshaft position do not vary by more than the first predetermined amount, the methodology proceeds to decision block  228 .  
         [0027]    In decision block  228 , the methodology compares the actual crankshaft position to the reference crankshaft position and determines if they vary from one another by more than a second predetermined amount.  
         [0028]    If the actual crankshaft position and the reference crankshaft position vary by more than the second predetermined amount, the methodology proceeds to block  232  wherein a second fault code is generated. The methodology then proceeds to block  236  wherein the crankshaft reference position and the series of combustion events are employed to control a plurality of crankshaft dependent operations. The method then loops back to block  204 .  
         [0029]    While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the description of the appended claims.