Abstract:
A method of correcting a cam phaser system failure including detecting a cam phaser system fault and generating a control signal to correct said cam phaser system fault.

Description:
TECHNICAL FIELD 
     The present invention relates to the control of a cam phaser used in an internal combustion engine. More specifically, the present invention relates to a method and apparatus for detecting and correcting a cam phaser or cam phaser solenoid fault. 
     BACKGROUND OF THE INVENTION 
     A cam phaser is a device to create a variable rotational offset between the exhaust camshaft, intake camshaft and crankshaft of an internal combustion engine (ICE). The degree of rotational offset generated by a cam phaser enables the ICE to be tuned for specific performance requirements by varying valve overlap, i.e., overlap between the exhaust and intake valves of an ICE. In applications where idle quality is important, a relatively small degree of valve overlap is desired. In applications where it is required that NOx components are reduced, a relatively large amount of overlap is desired. The cam phaser provides charge dilution in the form of recirculated exhaust gases. Charge dilution is a method of adding inert substance to the air/fuel mixture in a cylinder of an ICE to decrease the heat capacity of the air/fuel mixture and thus reduce the amount of NOx components. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method and apparatus for detecting a faulted cam phaser and correcting the fault. The cam phaser in the present invention is a hydraulic continuously variable cam phaser coupled to the exhaust valve cam shaft of an overhead cam ICE, but any engine configuration is considered within the scope of the present invention. In alternate embodiments of the present invention, the cam phaser may be coupled to the intake valve camshaft. The cam phaser position is controlled by a pulse width modulated solenoid valve controlling the hydraulic fluid (oil) flow to an adjusting piston. The oil pressure acts in concert with a spring pushing the adjusting piston with a force that opposes the oil pressure. The combination of oil pressure and flow acting against the spring force positions the cam phaser, placing a camshaft and its associated valves in a desired position. 
     During certain operating conditions, a hydraulic cam phaser may be unable to maintain its commanded position due to debris in the oil jamming the solenoid armature or other similar conditions. Debris in the oil can prevent modulation of fluid flow to and from the cam phaser, preventing closed loop control of the cam phaser. 
     The present invention includes a method and apparatus to determine when the cam phaser solenoid is stuck or jammed in position and a method and apparatus to release or unstick the cam phaser solenoid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic drawing of a preferred cam phaser system of the present invention. 
         FIG. 2  is a flow chart of a preferred solenoid release detection method of the present invention. 
         FIG. 3  is a flow chart of a preferred solenoid release output control method of the present invention. 
         FIG. 4  is a flow chart of a preferred solenoid release active move reset method of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a diagrammatic drawing of a cam phaser system  10  of the present invention. The cam phaser system  10  is provided with pressurized hydraulic fluid such as oil by an oil pump  12  and an oil filter  14 . A four-way solenoid valve  16  controls the oil flow to a cam phaser  18 . The solenoid valve  16  is controlled by a powertrain control module  15  to pulse width modulate (PWM) the four-way valve  16 . The cam phaser  18  is coupled between a camshaft sprocket and the end of the camshaft. The camshaft sprocket is coupled to the crankshaft, as is commonly known in the art. 
     The cam phaser  18  includes a piston  20  and spring  24  that are acted upon by oil pressure to move the piston  20  in the directions of arrow A. The sliding piston  20  will rotate sliding helical gears on the sprocket and camshaft to rotate the camshaft relative to the cam shaft sprocket and produce the variable cam phaser functionality of the present invention. Oil pressure and flow is provided via the solenoid valve  16  to act upon both sides of the piston  20 . The spring  24  opposes movement of the piston  20  in one direction. The movement of the piston  20 , and thus the cam phaser  18 , will be controlled by the oil flow to either side of the piston  20 . The camshaft further includes target wheel and sensors  30 ,  32  to detect the speed and position of the camshaft and/or crankshaft and provide feedback for a camshaft position algorithm. 
     The amount of oil flow to the piston  20  is controlled by the modulation of the solenoid valve  16 . The powertrain controller  15  controls the duty cycle of the solenoid valve  16  to generate the desired position of the piston  20  and thus the cam phaser  18 . In certain situations, debris in the oil may restrict the solenoid valve  16 , preventing the modulation of oil flow through the solenoid. Depending on operating conditions, the inability to modulate oil flow will result in uncontrolled movement of the cam phaser  18 , or inability to move the cam phaser  18 . The method and apparatus of the present invention will detect this jammed condition and generate a control current of cyclic output to the solenoid valve  16  to jar the debris loose and release the solenoid  16 . 
       FIGS. 2 ,  3  and  4  are flowcharts of preferred methods of the present invention. As the cam phaser  18  velocity and direction are related to solenoid position, and since the solenoid  16  can stick in any position, cam phase angle is difficult to use as an indication of a sticking solenoid. The present invention uses error counts (time) of two cam phase angle correlation diagnostic to determine if the solenoid  16  is stuck or jammed. Once this determination has been made, the controller  15  will apply a cyclic current output to the solenoid  16  to allow the debris or other sticking conditions to be released. The output is preferably applied at a rate that prevents the cam phaser  18  from responding to the cyclic current output once the solenoid  16  has been released. The parameters of the cyclic output are preferably calibrated to ensure that enough force can be applied to release the solenoid  16 , while keeping the frequency high enough to prevent the cam phaser  18  from responding and creating another position error. 
       FIG. 2  is a flow chaff of a preferred solenoid release detection method of the present invention. The software routine of the present invention at block  50  determines if the controller  15  has provided a cyclic current output to the solenoid  16  to unstick the solenoid  16  at the current commanded cam phaser  18  position. This determination is made by checking the flag set at block  50 . The application of cyclic current to the solenoid  16  by the controller  15  will be termed as the “cycler” routine. The cycler routine may be executed only once per cam phaser  18  move. If the cycler has been active this cam phaser  18  move, then the routine will exit at block  100 . If the cyclor has not been active as this commanded cam phaser  18  position, the routine will continue to block  52  to determine if the cycler has been activated more than a certain calibrated number of times in this ignition cycle. If the cycler has been active more than the calibrated number of times in this ignition cycle, then the routine will exit at block  100  to allow the diagnostic to complete and indicate that there is a mechanical or engine problem. If the cycler has not been active more than the calibrated number of times in this ignition cycle, the routine will continue to block  54 . 
     Block  54  represents a diagnostics routine (P0016) to detect a cam phaser  18  home position fault. The P0016 diagnostic runs when the cam phaser  18  is commanded to its home (fully advanced) position. The diagnostic compares the current position of the cam phaser  18  to its design intent home position. If these positions vary by more than a calibrated amount, the cam phaser is determined to be stuck and the P0016 diagnostic failure counter (timer) will increment. If the condition remains for a calibrated amount of time, the diagnostic will log a failure of this condition in the controller  15  and will disable the operation of the cam phaser  18 . The P0016 diagnostic is determined to have been passed (i.e., diagnostic indicates no faults) when the current cam phaser  18  position is within a calibrated range of the design intent home position for a calibrated amount of time. If a cam phaser  18  fault has been detected by block  54 , the routine will continue to block  58 . 
     The fault detection at block  54  occurs at a lower calibrated time, than failure of the P0016 diagnostic, and therefore before a cam phaser  18  fault is logged or cam phasing is disabled. If a cam phaser  18  fault has not been detected at block  54 , the routine will continue to block  56  having a second diagnostics routine (P0014). The P0014 diagnostic runs when the cam phaser  18  is commanded to any position other than its home (fully advanced) position. The diagnostic compares the current position of the cam phaser  18  to its commanded position. If these positions vary by more than a calibrated amount, the cam phaser is determined to be faulted and the P0014 diagnostic failure counter (timer) will increment. If the condition remains for a calibrated amount of time, the diagnostic will log a failure of this condition in the controller  15  and will disable operation of the cam phaser  18 . The P0014 diagnostic is determined to have passed when the current cam phaser  18  position is within a calibrated range of the commanded cam phaser  18  position for a calibrated amount of time. If no cam phaser fault is detected at block  56 , the routine will end at block  100 . If a cam phaser fault has been detected at block  56 , the routine will continue to block  58 . The fault detection at block  56  occurs at a lower calibrated time, than failure of the P0014 diagnostic, and therefore before a cam phaser  18  fault is logged before cam phasing is disabled. 
     The routine, at block  58 , sets a flag to indicate that the cyclic output should be enabled and continues to block  60  to set a flag indicating that the cycler has been activated at this commanded cam phaser  18  position. The flag set at block  60  will prevent the cycler from being activated again until the cam phaser  18  is commanded to a new position. Continuing to block  62 , the routine increments a first counter that indicates how many times the cycler has been activated in this specific ignition cycle. The cycle counter at block  64  is initialized to allow the cycler to perform a calibrated number of square wave PWM cycles to release the sticking solenoid  16 . 
     Once a cam phaser fault has been detected by the algorithm in  FIG. 2 , the software routine to release the solenoid  16  is activated.  FIG. 3  is a flow chart of a preferred solenoid release control software routine of the present invention. Starting at block  80 , the routine will determine if the solenoid release routine should be active. The flag set at block  58  will indicate if the solenoid release routine should be active. If the flag has not been set, the routine will return to normal closed loop control for the cam phaser  18  at block  82 . Block  84  determines if the number of release cycles or current pulses initialized to a calibrated value at  64  have been completed, as determined by a first counter. The first counter indicates the number of square wave PWM output cycles remaining to be completed by the cycler. If the calibrated number of square wave PWM cycles are complete as indicated by the first counter being zero, then the solenoid release routine will be stopped at block  86  by clearing the flag set at block  58  and checked at block  80 , and the cam phaser  18  will be returned to normal closed loop control at block  82 . 
     Continuing to block  88 , when the release cycles have not been completed, block  88  determines if the output of the controller (“control signal ”) to tile solenoid  16  should be in a high or on position for the current output cycle. This determination is made by comparing a second counter to a calibrated desired high time. If the control signal should be high, then the second counter is incremented at block  90  and the control signal is forced to a high condition for the current output cycle at block  92 . The routine then exits at block  94 . If the controller determines that the control signal for the current output cycle should not be high, the routine continues to block  96 . Block  96  determines if the control signal should be low or off. This determination is made by comparing a third counter to a calibrated desired low time. If the control signal should not be low, the second and third counters are reset at block  98  and the first counter is incremented at block  100 . The routine will then continue to block  84 . 
     If the controller determines that the control signal should be low at block  96 , the third counter will be incremented at block  102  and the control signal will be forced to a low condition for the current output cycle at block  104 . The routine will then exit at block  94 . The routine of  FIG. 3  will thus modulate a control signal to the solenoid that will be held high and low for a certain calibrated amount of time and a certain calibrated number of cycles to release the solenoid  16  from a jammed or stuck condition. 
       FIG. 4  is a flow chart of a preferred routine to clear the flag that indicates that the cycler has been active at the current desired cam phaser  18  position of the present invention. The routine starts at block  110 . At block  112 , the routine determines if the commanded cam phaser  18  position has changed. This determination is made by comparing the current commanded position to the previous commanded position. If the commanded position has changed, execution continues at block  114 . The flag to indicate that the cycler has been active at the current commanded cam phaser  18  position is cleared at block  114 . This action allows the cycler to be made active again at the current commanded cam phase position if necessary. This flag is checked at block  60  in FIG.  2 . If the commanded cam phaser  18  position has not changed from the previous position, as determined in block  112 , the routine exits at block  116 . 
     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.