Abstract:
False spark knock detection is minimized for a displacement on demand engine having activated and deactivated modes. The engine is operated in the activated mode. Knock detection is performed on all cylinders of the engine during the activated mode. The engine is operated in the deactivated mode. Knock detection is performed on activated cylinders during the deactivated mode. Knock detection is disabled for deactivated cylinders during the deactivated mode.

Description:
FIELD OF THE INVENTION 
     The present invention relates to displacement on demand engines, and more particularly to a control system for detecting spark during displacement on demand transitions. 
     BACKGROUND OF THE INVENTION 
     Displacement on Demand (DOD) engines deactivate one or more cylinders when full engine power is not needed. Running on fewer cylinders reduces pumping losses and improves fuel economy. An engine control system transitions from a deactivated mode to an activated mode when full power is required or for stability as the engine nears idle. 
     Spark knock is caused by auto-ignition of a fuel/air mixture in the cylinders. High pressure waves propagate and cause an audible “knocking” sound. Audible spark knock causes customer dissatisfaction and can lead to engine damage. Some engine control systems detect spark knock and vary spark advance to reduce spark knock. A knock sensor monitors a knock frequency in each cylinder during part of the power stroke. 
     The output of the knock sensors provides an instantaneous noise value (INST). Knock occurs when the instantaneous noise value exceeds a knock threshold (TH). The difference between the instantaneous noise value and the threshold determines a knock intensity, which is used to reduce spark. A mean average deviation (MAD) is calculated based on the difference between the average and the instantaneous noise values. The updated MAD values are used to calculate the knock threshold for the subsequent combustion event for the cylinder. 
     The knock threshold defines a boundary between acceptable noise (no knock) and unacceptable noise (knock). The filtered instantaneous noise (INST) value is used to vary the gain of a band pass filter (BPF). The gain is used to increase or attenuate knock depending on the value of background noise. 
     An exemplary method for controlling spark knock is shown in FIG.  1 . Spark knock control  10  begins with step  12 . In step  14 , control determines if the engine is operating. If the engine is operating, control measures an instantaneous noise in step  16 . If the engine is not operating, control ends in step  52 . In step  16 , an instantaneous noise value is measured. In step  18 , control determines if knock is present. If knock is present, a current average for knock is updated in step  22 . If knock is not present, a current average for no knock is updated in step  20 . The average calculations are represented by the following exemplary formulas: 
     For no knock: 
     
       
           AVE   current   =AVE   prior +[( INST−AVE   prior )( FC )] 
       
     
     For knock: 
     
       
           AVE   current   =AVE   prior +[( INST−AVE   prior )( FC )( KM )] 
       
     
     where FC is a detection filter coefficient and (KM) is a knock multiplier. The (KM) is applied to minimize the effect of a large instantaneous value. 
     If no knock is detected, control determines if the instantaneous noise value is less than the average noise value in step  24 . If the instantaneous noise value is less than the average noise value, a new MAD value is calculated in step  26 . An exemplary MAD calculation is represented by the following exemplary formula: 
     
       
           MAD=MAD   PREV (1 −Filt Coeff )+( AVE   current   −INST )( Filt Coeff ) 
       
     
     MAD is calculated using a first order lag filter. A new threshold is determined in step  28 . An exemplary threshold is represented by the following formula: 
     
       
           TH=AVE   current +( MAD   current )( MAD   mult ) 
       
     
     where MAD mult  is a MAD multiplier. The MAD multiplier is a function of engine speed and load. In step  30 , control determines if knock is present. If knock is present, a current knock gain average is updated in step  36 . If knock is not present, a current no knock gain average is updated in step  32 . The gain average calculations are represented by the following exemplary formulae: 
     For no knock: 
     
       
         GAINAVG current =GAINAVG prior +[( INST −GAINAVG prior )( FC   gain )] 
       
     
     For knock: 
     
       
         GAINAVG current =GAINAVG prior+[(   INST −GAINAVG prior )( FC   gain )( KM   gain)]   
       
     
     where FC gain  is a gain average filter coefficient and (KM gain ) is a gain average knock multiplier. 
     In step  40  control determines if GAINAVG current  is greater than a maximum GAINAVG threshold. If GAINAVG current  is greater than the maximum GAINAVG threshold, the knock signal gain is decreased in step  48  and control returns in step  50 . If GAINAVG current  is not greater than a maximum GAINAVG threshold, control determines if GAINAVG current  is less than a minimum GAINAVG threshold in step  44 . If GAINAVG current  is less than a minimum GAINAVG threshold, the knock signal gain is increased in step  46  and control ends in step  50 . If GAINAVG current  is not less than a minimum GAINAVG threshold, control returns in step  50 . The equations set forth with respect to AVE current , MAD current , and GAINAVG current  are hereinafter collectively referred to as “the knock equations”. The knock equations are updated for each firing event in each cylinder. 
     Performing knock detection on a DOD engine presents potential drawbacks. When cylinders are deactivated, the running cylinders operate at a higher load, which increases the combustion noise of the running cylinders. While the deactivated cylinders contribute no spark knock noise, background and mechanical noise is detected from the knock sensors that are associated with the deactivated cylinders. The measured noise reduces the average value of the deactivated cylinders. When the deactivated cylinders are reactivated, the threshold is artificially low based on the reduced average value. Acceptable noise may be incorrectly characterized as spark knock, resulting in false retard. 
     SUMMARY OF THE INVENTION 
     A method according to the invention minimizes false spark knock detection for a displacement on demand engine having activated and deactivated modes. The engine is operated in the activated mode. Knock detection is performed on all cylinders of the engine during the activated mode. The engine is operated in the deactivated mode. Knock detection is performed on activated cylinders during the deactivated mode. Knock detection is disabled for deactivated cylinders during the deactivated mode. 
     A method according to the invention minimizes false spark knock detection for a displacement on demand engine having activated and deactivated modes. The engine is operated in the activated mode. A knock threshold is established. Knock detection is performed on all cylinders of the engine during the activated mode using the knock threshold. The engine is operated in the deactivated mode. The knock threshold is increased for the transition period. Knock detection is performed on all cylinders of the engine during the deactivated mode using the increased knock threshold. 
     A method according to the invention minimizes false spark knock detection for a displacement on demand engine having activated and deactivated modes. A noise value is measured in each cylinder of the engine. A threshold knock value is established based on the measured noise value for each cylinder of the engine. One or more cylinders are deactivated. The noise in the deactivated cylinders is frozen and ignored. The deactivated cylinders are reactivated. The threshold knock value is updated for the deactivated cylinders based on the measured noise values from activated cylinders. Knock is determined for the reactivated cylinders based on the updated threshold. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a flowchart illustrating prior art steps of performing knock detection; 
     FIG. 2 is a functional block diagram of an engine control system that minimizes false spark knock detection for DOD engines according to the present invention; 
     FIG. 3 is a flowchart illustrating steps for minimizing false spark knock detection during cylinder deactivation for a DOD engine according to a first method of the present invention; 
     FIG. 4 is a flowchart illustrating steps for minimizing false spark knock detection during cylinder deactivation for a DOD engine according to a second method of the present invention; 
     FIG. 5 is a flowchart illustrating steps of performing the modified spark knock detection of FIG. 4; and 
     FIG. 6 is a flowchart illustrating steps for minimizing false spark knock detection during cylinder deactivation for a DOD engine according to a third method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, activated refers to operation using all of the engine cylinders. Deactivated refers to operation using less than all of the cylinders of the engine (one or more cylinders not active). The present invention applies to engines having various cylinder configurations such as 4, 6, 8, 10, 12 and 16 cylinders. 
     Referring now to FIG. 2, an engine control system  110  according to the present invention includes a controller  112  and an engine  116 . The engine  116  includes a plurality of cylinders  118  each with one or more intake valves and/or exhaust valves (not shown). The engine  116  further includes a fuel injection system  120  and an ignition system  124 . An electronic throttle controller (ETC)  26  adjusts a throttle area of an intake manifold  28  based upon a position of an accelerator pedal (not shown) and a throttle control algorithm that is executed by the controller  112 . One or more sensors  134  and  132  such as a manifold pressure sensor and/or a manifold air temperature sensor sense pressure and/or air temperature in the intake manifold  128 . The controller  112  receives pedal position information from brake and accelerator pedal position sensors  130  and  140 . An output of the engine  116  is coupled by a torque converter clutch  154  to a transmission  158 . 
     An Electronic Spark Control (ESC) system  122  communicates with the knock sensors  138  and  148  located adjacent to the banks  134  and  144  of the engine  116 . While the ESC system  122  is shown within the controller  112 , it will be appreciated that the ESC system  122  and the controller  112  may include one or more controllers. In addition, while the knock sensors  138  and  148  are associated with the cylinder banks  134  and  144 , respectively, it will be appreciated that alternative configurations may be used. For example, one knock sensor for each cylinder may be used or alternatively one sensor for the whole engine. 
     The controller  112  determines the cylinder  118  that is currently being fired. A multiplexer (MUX)  142  communicates with the controller  112  and determines the knock sensor  138  or  148  output that should be used for the current fired cylinder. For example, if a first cylinder  118  is fired in the bank  134 , the MUX  142  uses an instantaneous noise value reading from the knock sensor  138 . During deactivation, the ESC system  122  disregards the signal from the deactivated cylinders and performs calculations on the cylinders that are fired. 
     During normal engine operation, the ESC system  122  receives information based on noise detected at the knock sensors  138  and  148 . The ESC  122  uses the information to control the spark knock by varying spark advance. In general, spark knock is declared when an instantaneous noise value (INST) exceeds a threshold (TH) value. This may be characterized by the following exemplary formula. 
     
       
         Knock=( INST )−( TH ) 
       
     
     As a result, if a knock value is greater than 0, then the knock value is used to calculate the amount of spark retard that is needed to suppress the knock in that cylinder. In one embodiment, the spark retard is proportional to the knock value. 
     With reference now to FIG. 3, steps for detecting spark for a DOD engine according to a first method are shown generally at  156 . In the first method, knock detection is performed for activated but not deactivated cylinders. Control begins in step  160 . In step  164 , control sets a current cylinder index equal to 1. In step  168 , control determines if the cylinder identified by the cylinder index is in deactivated mode. If the identified cylinder is in deactivated mode, control determines if the cylinder index is equal to the number of cylinders (N) in the engine  16  in step  170 . If the identified cylinder is not in deactivated mode, control performs knock detection in step  10  (FIG.  1 ). If the cylinder index is equal to the number of cylinders (N) in the engine  116 , control ends in step  180 . If the cylinder index is not equal to the number of cylinders in the engine  116 , the cylinder index is incremented by one in step  178  and control loops back to step  168 . 
     Turning now to FIG. 4, steps for detecting spark for a DOD engine according to a second method are shown generally at  166 . The spark detecting method  166  includes similar steps as described with respect to spark detection method  156 . In the second method, a modified spark knock detection is performed for deactivated cylinders in step  174 . 
     The modified spark knock detection  174  is shown in FIG.  5  and includes similar steps as knock detection  10  in FIG.  1 . However, in step  188 , a modified knock threshold is established to raise the threshold. The modified knock threshold may be characterized by the following formula; 
     
       
           TH   raised   =AVE   current +( MAD   current )( MAD   mult +TransOffset) 
       
     
     where TransOffset is a transient offset and a function of engine RPM. 
     With reference now to FIG. 6, steps for detecting spark for a DOD engine according to a third method are shown generally at  200 . In the third spark detection method  200 , the knock equations for each deactivated cylinder are updated using values from adjacent activated cylinders when transitioning from deactivated to activated mode. Spark detection begins in step  212 . In step  216 , control determines if the engine  116  is transitioning from deactivated mode to activated mode. In step  220 , a cylinder index is set equal to 1. If the engine  116  is not transitioning to activated mode, control loops to step  216 . If the engine  116  is transitioning to activated mode, control determines if the cylinder identified by the cylinder index is a deactivated cylinder in step  222 . If the identified cylinder is not a deactivated cylinder, knock detection is performed in step  10  (FIG.  1 ). If the identified cylinder is a deactivated cylinder, the knock equations are updated with adjacent activated cylinder knock detection values in step  226 . 
     In step  230 , control determines if the cylinder index is equal to the number of cylinders (N) in the engine  116 . If the cylinder index is equal to the number of cylinders (N) in the engine  116 , control ends in step  240 . If the cylinder index is not equal to the number of cylinders in the engine  116 , the cylinder index is incremented by 1 in step  232  and control loops back to step  222 . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.