Abstract:
A method and apparatus for determining the switching states of a target wheel used in an internal combustion engine, the method including providing a camshaft, providing a target wheel having teeth coupled to the camshaft, providing a sensor to detect the teeth of the target wheel, providing a cam phaser to phase the camshaft relative to a crankshaft of the internal combustion engine, homing the cam phaser to a known position relative to the crankshaft, rotating the crankshaft and camshaft, detecting the switching of the teeth by the sensor, referencing switching information detected by the teeth to crankshaft position information to produce a calibration for the target wheel, and storing the calibration in a controller to be use for control of the internal combustion engine.

Description:
TECHNICAL FIELD 
     The present invention relates to the control of an internal combustion engine. More specifically, the present invention relates to calibrating target wheels for speed, timing, and position sensing systems used in internal combustion engines. 
     BACKGROUND OF THE INVENTION 
     Presently, automotive companies manufacture data or target wheels for use with speed sensors to detect the speed, timing, and position of an engine crankshaft and/or a camshaft. As is known in the art of four-cycle internal combustion engines (ICEs), position and timing between a crankshaft and a camshaft is very important for the application and synchronization of spark and fuel, as the camshaft actuates the intake and exhaust valves of an ICE. A camshaft may be used in an overhead valve (OHV) configuration where the valves are actuated via pushrods, or in an overhead cam (OHC) configuration where the valves are acted on directly by the camshaft. The camshaft is driven by the crankshaft through a 1:2 reduction (i.e., two rotations of the crankshaft equal one rotation of the camshaft) and the camshaft speed is one-half that of the crankshaft. The crankshaft and camshaft position, for engine control purposes, are measured at a small number of fixed points, and the number of such measurements may be determined by the number of cylinders in the ICE. 
     As previously described, engine control systems use the timing and position information supplied by a crankshaft and camshaft sensor for controlling the application of spark and fuel to the cylinders of an ICE. The position and timing (phase) of a first camshaft controlling exhaust valves for a cylinder and/or a second camshaft controlling intake valves for a cylinder in an overhead cam engine may be controlled relative to the crankshaft (piston position) to reduce emissions and improve fuel economy. Several cam-phasing devices (cam phasers) exist in today&#39;s automotive market that require accurate position and timing information provided by the camshaft position sensor. The crankshaft and/or camshaft position sensor typically include a variable reluctance or Hall effect sensor positioned to sense the passage of a tooth, tab and/or slot on a target or data wheel coupled to the camshaft. 
     The target or data wheel used with present camshaft position sensors have a distribution of teeth, tabs and/or slots. The camshaft position sensor typically comprises a variable reluctance or Hall effect sensor positioned to sense the teeth on a target or data wheel coupled to the camshaft. The magnetic properties and material composition of the target wheel will vary where and when the sensor senses the teeth on a moving target wheel. This variation may cause problems in the feedback provided by the sensor. For example, two target wheels with identical footprints but made of different materials will have different magnetic and switching characteristics. Referring to FIG. 1, a sensor  18  is positioned to sense the teeth  40 / 41  of target wheel  23 . For a first material, the sensor may switch at point A and for a second material the sensor  18  may switch at point B. The varying material compositions that happen during manufacturing processes even within the same “batch” of target wheels produced in the same factory may lead to an inconsistency in sensing or switching. This difference in switching between point A and point B will adversely affect the ability to predict the switching position of the sensor  18  and program or calibrate the control of an ICE. Thus, there is a need to better determine the magnetic and switching characteristics for a target wheel to more accurately control an ICE. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a target wheel calibration method and apparatus used to detect camshaft and crankshaft timing, position and speed for a four-cycle internal combustion engine (“ICE&#39;”). The present invention utilizes a method of detecting the position of a target wheel tooth (or teeth) at a known position relative to the crankshaft and camshaft. The method comprises zeroing/homing a cam phaser coupled to the target wheel and camshaft and then rotating the crankshaft through two revolutions (thereby rotating the camshaft one revolution) to determine where the teeth of the target wheel switch the sensor. The switching time and position of the teeth of the target wheel on the camshaft are referenced to the target wheel pulse train of the crankshaft. The switching position of the target wheel on the camshaft is thus “known” with respect to the position of the crankshaft and corresponding cylinder events. This position and timing information is stored and referenced by a controller to control the functions of the ICE. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various advantages of the present invention will become apparent to one skilled in the art upon reading the following specification and by reference to the drawings in which: 
     FIG. 1 is a diagrammatic drawing illustrating the variation in switching properties that may occur with target wheels; 
     FIG. 2 is a diagrammatic drawing of the engine and control system of the present invention; 
     FIGS. 3 and 4 are diagrams of the preferred embodiments of target wheels used in the present invention; 
     FIG. 5 is a timing diagram illustrating the signals generated by the target wheels of the present invention; and 
     FIG. 6 is a flowchart of the preferred method of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 2, an internal combustion engine (ICE)  10  having a crankshaft  12  generates a pulse train via the rotation of a target wheel  15  on the crankshaft  12  sensed by a conventional wheel speed sensor  16 . The wheel speed sensor  16  may comprise any known wheel speed-sensing device including, but not limited to, variable reluctance sensors, Hall effect sensors, optical switches, and proximity switches. The purpose of the wheel speed sensor  16  is to detect the teeth on the target wheel  15  and provide the pulse train to an electronic controller  22 . The electronic controller  22 , in conjunction with other sensors, will determine the speed and position of the crankshaft  12  using the pulse train generated by the speed sensor  16 . 
     The vehicle controller  22  may be any known microprocessor or controller used in the art of engine control. In the preferred embodiment, the controller  22  is a microprocessor, having nonvolatile memory NVM  26  such as ROM, EEPROM, or flash memory, random access memory RAM  28 , and a central processing unit (CPU)  24 . The CPU  24  executes a series of programs to read, condition, and store inputs from vehicle sensors. The controller  22  uses various sensor inputs to control the application of fuel and spark to each cylinder through conventional spark and fuel injector signals  30 . The controller  22  further includes calibration constants and software stored in NVM  26  that may be applied to control numerous engine types. 
     In the preferred embodiment of the present invention, the ICE is equipped with an exhaust camshaft  14  and intake camshaft  19 . The exhaust camshaft  14  and intake camshaft  19  are coupled to the crankshaft  12  via a timing belt or chain  25  and sprockets coupled to the camshafts  14 ,  19 . The exhaust camshaft  14  actuates exhaust valves for the cylinders, and the intake camshaft  19  actuates intake valves for the cylinders, as is commonly known in the art. A target wheel  23  coupled to the exhaust camshaft  14  generates periodic signals using wheel speed sensor  18  to provide speed and position information for the exhaust camshaft  14 . The wheel speed sensor  18  may be similar in functionality to wheel speed sensor  16 . 
     The present invention may further be equipped with a continuously variable cam phaser  32 , as is known in the art. The cam phaser  32  in the preferred embodiment is coupled to the exhaust camshaft  14 . In alternate embodiments of the present invention, a cam phaser may be coupled to the intake camshaft  19  or to both the exhaust and intake camshafts  14 ,  19 , or a common intake/exhaust cam depending on the desired performance and emission requirements of the ICE  10 . The cam phaser  32  is preferably hydraulically modulated to create a variable rotational offset between the exhaust camshaft  14  and the intake camshaft  19  and/or the crankshaft  12 . The degree of rotational offset generated by the cam phaser  32  enables the ICE  10  to be tuned for specific performance requirements by varying valve overlap, i.e., overlap between the exhaust and intake valves of the ICE  10 . In applications where it is required that NOx components are reduced, the cam phaser  32  can provide charge dilution in the form of recirculated exhaust gases. Charge dilution is a method of adding an inert substance to the air/fuel mixture in a cylinder of the ICE  10 . The inert substance will increase the heat capacity of the air/fuel mixture and reduce the amount of NOx components created during combustion. Accordingly, by regulating the valve overlap area, NOx components may also be regulated. Furthermore, engine performance characteristics such as horsepower and fuel economy may also be modified using the cam phaser. For an ICE equipped with camshafts that operate both intake and exhaust valves, valve timing relative to the combustion cycle may be adjusted. 
     FIG. 3 is a diagram of the target wheel  23  of the preferred embodiment of the present invention that will be described in conjunction with a timing diagram of FIG.  5 . The target wheel  23  includes an irregular surface having teeth, slots, or tabs  40  and  41 . The teeth  40  are smaller in length than the teeth  41  to differentiate the intake and exhaust phases of the ICE  10 . The teeth  40  are fifteen degrees wide and are spaced forty-five degrees apart. The teeth  41  are forty-five degrees wide and are spaced fifteen degrees apart. The inner diameter of the teeth  40  and  41  is preferably 72 mm and the outer diameter is preferably 75 mm, generating a 3 mm tooth height for teeth  40  and  41 . The teeth  40  and  41  further include clearly defined edges for generating a pulse train for wheel position sensor  18 . 
     Referring to FIG. 4, the target wheel  15  and sensor  16  are shown. The target wheel  15  preferably has a diameter of 171.89 mm (approximately 4.0 mm wide) and includes fifty-eight teeth  44 . The teeth  44  are preferably three degrees apart and three degrees wide and are chamfered on the corners. The height of the teeth  44  is preferably 4.0 mm. The target wheel  15  further includes a fifteen degree-wide void  46  to provide a marker pulse for a complete revolution of the target wheel  15 . 
     Referring to FIG. 5, a timing diagram is shown with a pulse train  52  generated by the target wheel  15  and target wheel sensor  16 , a pulse train  54  generated by the target wheel  23  and target wheel position sensor  18 , an engine cycle reference  56 , and an engine position reference  58 . The pulse trains  52  and  54  include events that correspond to the physical layout of the teeth  40 / 41  of target wheel  23  and the teeth  44  of target wheel  15 . The pulse trains  52  and  54  signal the controller  22  the state of the exhaust camshaft  14  and the state of the crankshaft  12  (i.e., is it in the compression or exhaust phase) and corresponding cylinder events to allow the application of spark and fuel by the controller  22 . 
     In the preferred embodiment of the present invention, the pulse train  52  has been processed to provide a specific cylinder event for each specific pulse. For example, a six pulse period for pulse train  52  will correspond to a six cylinder engine, each pulse indicating the top dead center (TDC) or bottom dead center (BDC) position for the six cylinders. Referring to FIG. 5, the crankshaft  12  to camshaft  14  angle is determined from the following ratios: 
     
       
         
           C/D=E/F  
         
       
     
     Where C=the crankshaft-to-camshaft exhaust camshaft angle 
     D=the crankshaft period in degrees 
     E=the period between cylinder and cam events 
     F=the period between cylinder events 
     Where D=(720 degrees)/(the number of cylinders in the engine) 
     The method of the present invention can be described as first zeroing or homing the cam phaser  32  coupled to the target wheel  23  and then rotating the target wheel  23  one revolution such that teeth  40 / 41  generate the pulse train  54 . The individual pulses generated by the teeth  40 / 41  are referenced to pulses/cylinder events generated by the crankshaft  12  in the pulse train  52  and stored in the controller  22 . All camshaft  14  phase positions are thus referenced individually relative to the home position and cylinder events in the pulse train  52 . The position of the crankshaft  12  is known to be a certain number of counts from the void  46 . Accordingly, by zeroing the cam phaser  32  and learning the individual positions of the teeth  40 / 41  on startup, the sensor  18  (and sensor  16 ) will be able to reproduce a consistent signal from teeth  40 / 41  of target wheel  23 . Thus, the physical cam position relative to crank or cam phase may be determined while simultaneously negating effects of tooth to tooth variation on the calculation of the cam phase angle. 
     The preferred method of the present invention can be seen in FIG. 6 as a flowchart. Starting at block  100 , the cam phaser  32  is zeroed or homed to a known position relative to the crankshaft  12 . The crankshaft  12  is then rotated at least two revolutions at block  102 . The sensor  16  will generate pulses from the target wheel  15  coupled to the crankshaft  12 . The routine at block  104  will then register the timing and position of the pulses generated by the sensor  18  and target wheel  23  relative to the pulses generated by sensor  16 . The pulse trains  52  and  54  are thus referenced against each other. At block  106 , these timing and position values will be stored in the NVM  26  of the controller  22  to be used in the control of the ICE  10 . In the preferred embodiment of the present invention, the method will be executed whenever the cam phaser  32  is in the home position and new position values for a tooth will be filtered into the result of the detection of the tooth. This allows compensating for any variations that may be caused by temperature or other environmental conditions. In alternate embodiments of the present invention, the method can be executed at the initial startup of the ICE  10 , or the method may be executed when engine timing problems have been detected. 
     While this invention has been described in terms of some specific embodiments, it will be appreciated that other forms can readily be adapted by one skilled in the art. Accordingly, the scope of this invention is to be considered limited only by the following claims.