Abstract:
A method of sensing crankshaft position for use with an engine ( 16 ) having a combined starter/alternator assembly ( 18 ). The crankshaft position sensor assembly includes a tone ring ( 38 ) with a sensor ( 36 ), mounted near the rotor ( 30 ) of the combined starter/alternator assembly ( 18 ), that produces an initial crankshaft position signal. A bandpass filter ( 46 ) receives this initial signal and a cylinder identification input from a camshaft sensor ( 48 ) and filters the initial signal. Then, a gain limiter ( 54 ) performs an additional filtering process to produce a crankshaft rotational position signal. The filtered crankshaft position signal can then be input into a vehicle system controller ( 58 ) and an inner loop controller ( 60 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for sensing the crankshaft position on an internal combustion engine and more particularly on an engine having an induction type combined starter/alternator. This invention was made with Government support under Prime Contract No. DE-AC-36-83CH10093, Subcontract No. ZCB-4-13032-02, awarded by the Department of Energy. The Government has certain rights in this invention. 
     BACKGROUND OF THE INVENTION 
     For environmental and other reasons generally, there is a desire to provide for automotive vehicles that operate with propulsion system other than just a typical internal combustion engine. One such propulsion system contemplated is a purely electric vehicle. But since the technology for purely electrical vehicles is not yet practical, (e.g., there are limitations not desired by consumers), combining the electric drive with a somewhat more conventional internal combustion engine is one alternative being considered. With two drive systems in the hybrid vehicle, however, both drive systems, including the internal combustion engine, must be minimal in size. 
     One of the developments for reducing the overall space taken by the internal combustion engine and its accessories is to substantially reduce in size or even to eliminate the flywheel that normally mounts to the crankshaft at the rear of the engine and to locate a combined starter/alternator in this position. This will substantially reduce the space taken by separate conventional starters and alternators. For instance, an electric machine rotor of the starter/alternator can double as the conventional flywheel. 
     However, this now creates an electromagnetic interference (EMI) rich environment at the rear of the engine within which the crankshaft position is preferably sensed for the hybrid vehicle. The new system now requires that the sensor operate in the presence of strong electromagnetic fields beneath end turns of a stator and alongside an induction machine rotor. Current production technology, such as Hall effect or Variable Reluctance sensors (VRS), for sensing crankshaft position, then, is unusable in a combined starter/alternator system due to the significant EMI, which is not present at these levels in a conventional flywheel configuration. 
     To overcome this, one could relocate current crankshaft position sensors to the front of the internal combustion engine, but then the desired resolution of the crankshaft position for this hybrid configuration would be lost. This resolution is needed to more accurately control an indirect field oriented induction machine, thus making relocation an inadequate solution. Consequently, there is a desire to allow for accurate crankshaft position sensing even in an EMI rich field created by an engine with a combined starter/alternator mounted at its rear. 
     SUMMARY OF THE INVENTION 
     In its embodiments, the present invention contemplates a method of determining a crankshaft position for a rotating crankshaft in an internal combustion engine having a combined starter/alternator and a camshaft. The method comprises the steps of: rotating the crankshaft; rotating a tone wheel with indications thereon at the same angular velocity as the crankshaft; sensing the indications on the tone wheel, from a first location, as they rotate; producing an initial crankshaft position signal; rotating the camshaft; sensing the rotational position of the camshaft; producing a camshaft rotational position signal; filtering the initial crankshaft position signal based upon the camshaft rotational position signal to produce a filtered crankshaft position signal; and gain limiting the filtered crankshaft position signal to produce a crankshaft rotational position signal. 
     Accordingly, an object of the present invention is to allow for a preferred location for crank position sensing at the rear of the engine when employing an induction type flywheel starter/alternator system. 
     A further object of the present invention is to allow for accurate signal determination by employing bandpass and tracking filters, for robust sensing in the EMI rich environment around the starter/alternator. 
     An advantage of the present invention is that a VRS or Hall Effect Sensor can accurately measure crankshaft position even when subjected to an EMI rich environment from a hybrid electric vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective view of a vehicle in accordance with the present invention; 
     FIG. 2 is an enlarged view of encircled area  2  in FIG. 1; 
     FIG. 3 is an exploded perspective view of encircled area  3  in FIG. 2; 
     FIG. 4 is a cross-sectional view of a flywheel starter/alternator in accordance with the present invention; 
     FIG. 5 is an enlarged perspective view of a tone ring and sensor as illustrated in the encircled area  5  in FIG. 3, rotated 180 degrees; 
     FIG. 6 is a block diagram of the circuit connected to the crankshaft position sensor in accordance with the present invention; 
     FIG. 7 is an exploded perspective view of the tone ring and sensor, similar to FIG. 3, in accordance with another embodiment of the present invention; 
     FIG. 8 is an enlarged view of the tone ring and sensor in accordance with the embodiment of FIG. 7; and 
     FIG. 9 is a view similar to FIG. 5, illustrating a further embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 illustrate a schematic of a portion of a hybrid electric vehicle  10  including an electric drive system having an inverter  12  and a battery  14 . A transmission  20  is electrically connected to the inverter  12  and drive motors, not shown, in order to drive the front wheels  22 . The vehicle  10  also includes a transversely mounted internal combustion engine  16 , for supplying power, when needed, to charge the battery  14 . Affixed to the back end of the engine  16 , and driven by a rear hub portion of an engine crankshaft  26  is a starter/alternator assembly  18 . This assembly  18  can act as a starter for the engine  16  and also can convert the output of the engine  16  into the electrical power that charges the battery  14 . 
     FIGS. 3-5 better illustrate the starter/alternator assembly  18 . As discussed above, in order to allow for two drive systems in a hybrid electric vehicle, each must be as compact as possible. The combined starter/alternator  18  is built in an annular volume around a coaxial twin plate dry clutch  32 . It includes a housing, illustrated as a bell housing  24   a  in FIG.  4  and as an open housing  24   b  in FIG.  3 . The housing  24   a  or  24   b  mounts to the engine block  17  at the rear of the engine  16 , around the end of the crankshaft  26 . 
     Rotationally fixed to the inner wall of the housing  24  is a stator  28 , and rotationally mounted radially within the stator  28  is a rotor  30 . The rotor  30  connects to a first side of the clutch assembly  32 . The second side of the clutch assembly  32  connects to the crankshaft  26 . When the starter/alternator assembly  18  is acting as a starter, the first side is the driving side and the second side of the clutch  32  is the driven. When the starter/alternator assembly  18  is acting as an alternator, the second side of the clutch  32  is the driving side and the first side is the driven. 
     Given the compact configuration of the starter/alternator assembly  18 , and hence the small diameter clutch assembly  32 , a conventional crankshaft position sensor would need to be located at a short radius, requiring the sensor to be located in either the engine&#39;s oil pan or inside the engine block  17  near the engine&#39;s rear seal. With the present invention however, a crankshaft position sensor  36  is located at an intermediate radial distance from the crankshaft  26  such that it is physically possible to locate it facing into the rotor  30  and be accessible from outside the engine block  17  and oil pan. Preferably, this sensor  36  is either a variable reluctance sensor or a Hall Effect sensor. 
     For this location of the crankshaft position sensor  36 , instead of employing holes in a flywheel as in a conventional configuration, a special tone ring  38  is employed. The tone ring  38  is preferably fabricated of lamination steel, having windows  40  cut out that approximate the slot/tooth dimensions preferred for the particular crankshaft position sensor  36  employed. The tone ring  38  illustrated herein shows a window arrangement in a conventional  36 - 2  pattern around its perimeter in proportions generally desirable for a VRS or Hall Effect sensor. Preferably, the inside radius  42  of the tone ring  38  matches the radius of the rotor  30 , and the tone ring radial depth matches the end ring depth of the rotor  30 . As for mounting, the tone ring  38  can be affixed to the rotor end ring during rotor aluminum cage casting. 
     Turning now to FIG. 6, the crankshaft position sensor  36  and signal processing components are illustrated. These components act to extract the corrupted VRS crankshaft position signal from the EMI generated by the starter/alternator  18 , illustrated in FIGS. 1-4. 
     Electromagnetic noise is created due to the magnetic coupling from the end turns of the stator  28  and similar fields from the rotor  30 . This noise introduces a common mode component into the crankshaft position signal. (This is illustrated in phantom in FIG. 6 as stator interference and rotor interference being added to the VRS crankshaft position signal.) Additionally, the high end-ring tangential magnetic field intensity drives the tone ring  38  into saturation in special regions where the peaks of the slip current occur, and the mechanical drive frequency effect causes the crankshaft position signal to be amplitude modulated, (blurring of the tone ring windows  40 ). The signal processing components described below correct for these errors. 
     The crankshaft position sensor  36 , which is located in proximity to the passing windows  40  on the tone ring  38 , is electrically connected to a bandpass filter  46 . The filter  46  also receives input from a camshaft cylinder identification sensor  48 , through an adjustment multiplier  50  that accounts for the difference in rotational speed between a crankshaft and a camshaft. The camshaft sensor  48  reads the information from a camshaft wheel  52 , as in conventional engines. The bandpass filter  46  then, is preferably of the switched capacitor type in which the center of frequency is a multiple of the cylinder identification frequency, (i.e., tracks the expected tone ring frequency and is an electromagnetic clean signal). 
     The output of the bandpass filter  46  is an input to a gain limiter  54 , having another input for gain tracking  56 , allowing for extraction of the fundamental ( 36 - 2  tooth) tone wheel information and index pulse. The output of the gain limiter  54 , then, provides the filtered crankshaft rotational position signal, which is available as input to a vehicle system controller  58  and an inner loop controller  60  for the alternator/starter assembly  18 . 
     The general operation of the system will now be described. During engine cranking the starter/alternator  18  is energized in the cranking mode with the first side of the clutch  32  driving the second side. High torque is developed and the engine crankshaft  26  is accelerated from standstill. In this cranking mode, the starter/alternator  18  starts up under open loop control until a few pulses of a cylinder identification signal from the camshaft sensor  48  are multiplied, by the multiplier  50 , to match the passing frequency of the windows  40  in the tone ring  38 . The signal is then filtered through the bandpass filter  46  and the gain limiter  54 . Subsequently, the alternator/starter inner loop (indirect field orienter) enters closed loop control (field oriented control) by employing the signal from the inner loop controller  60 . Also, the filtered crankshaft position signal is sent to the vehicle system controller  58 , providing information for engine operation (such as ignition timing, etc.). 
     An alternate embodiment illustrating a tone ring and crankshaft position sensor is shown in FIGS. 7 and 8. In this embodiment, the crankshaft position sensor  36  remains the same although it is reoriented to account for a differently shaped tone ring  38 ′. For this tone ring  38 ′, the windows  40 ′ face radially outward (around a cylindrical outer surface rather than along a circular surface as in the first embodiment) and the crankshaft position sensor  36  faces radially inward toward the windows  40 ′. 
     Another embodiment is illustrated in FIG.  9 . In this embodiment an additional crankshaft position sensor  66 , again preferably a Hall Effect or VRS type, is mounted adjacent the tone ring, but circumferentially spaced from the first crankshaft position sensor  36 . Both of the crankshaft sensors will send a signal to the bandpass filter and can be used to generate a quadrature signal and hence double the position resolution. 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.