Abstract:
A diagnostic control system for an internal combustion engine including a discrete variable valve lift (DVVL) system includes a first module that determines a knock threshold value based on engine operating parameters and an engine knock sensor that generates a knock signal. A second module monitors a portion of the knock signal that is associated with a particular cylinder of the engine, selectively identifies a fault of at least one valve of the DVVL system associated with the particular cylinder based on the portion and the knock threshold, and outputs a fault signal corresponding to the particular cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/847,225, filed on Sep. 26, 2006. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to vehicle diagnostic systems, and more particularly to a discrete variable valve lift (DVVL) diagnostic system that determines a valve lift malfunction in a DVVL engine system. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Vehicles include an internal combustion engine that generates drive torque. More specifically, an intake valve is selectively opened to draw air into the cylinders of the engine. The air is mixed with fuel to form a combustion mixture. The combustion mixture is compressed within the cylinders and is combusted to drive pistons within the cylinders. An exhaust valve selectively opens to allow the exhaust gas to exit from the cylinders after combustion. 
     A rotating cam shaft regulates the opening and closing of the intake and exhaust valves. The camshaft includes a plurality of cam lobes that rotate with the camshaft. The profile of the cam lobe determines the valve lift schedule. More specifically, the valve lift schedule includes the amount of time the valve is open (duration) and the magnitude or degree to which the valve opens (lift). Manufacturers usually incorporate a fixed valve lift schedule for an engine since it may be suitable for a range of operating conditions. However, the fixed valve lift schedule may not be optimal during a particular engine operating condition. For example, during highway travel a vehicle may experience minimal acceleration. During such a condition, the engine may require less air per cylinder. However, when the engine operates on a fixed valve lift schedule excess air may be pumped into the engine cylinders, resulting in pumping losses of the engine. 
     A discrete variable valve lift (DVVL) system enables the engine to operate on more than one valve lift schedule. More specifically, a DVVL engine system switches between different valve lift schedules based on the operating conditions of the engine. This has been shown to minimize pumping losses of the engine. 
     A malfunction of the DVVL system may occur when a cylinder experiences differential valve lift. More specifically, differential valve lift occurs when a set of intake and/or exhaust valves of a particular cylinder operate on different valve lift schedules. In other words, the intake and/or exhaust valves of the cylinder are not synchronized. For example, a malfunction may occur when the DVVL engine system is operating in a high lift (HL) mode and one of the cylinders has an intake valve operating in a low lift (LL) mode and the other intake valve is operating in high lift (HL) mode. 
     SUMMARY 
     Accordingly, the present disclosure provides a diagnostic control system for an internal combustion engine including a discrete variable valve lift (DVVL) system. The diagnostic control system includes a first module that determines a knock threshold value based on engine operating parameters and an engine knock sensor that generates a knock signal. A second module monitors a portion of the knock signal that is associated with a particular cylinder of the engine, selectively identifies a fault of at least one valve of the DVVL system associated with the particular cylinder based on the portion and the knock threshold, and outputs a fault signal corresponding to the particular cylinder. 
     In another feature, the diagnostic control system further includes a third module that selectively limits engine speed when the fault is identified. 
     In another feature, the second module identifies the fault when the knock signal is greater than the knock threshold. 
     In another feature, the second module identifies the fault when an average value of the knock signal over a plurality of engine cycles exceeds the knock threshold. 
     In another feature, the second module identifies the fault when the knock signal exceeds the knock threshold a threshold number of times within a particular number of engine cycles. 
     In still another feature, the operating parameters include at least one of an engine speed, a manifold absolute pressure and an ambient air temperature. 
     In yet another feature, the diagnostic control system further includes a third module that selectively initiates a valve operating mode of the DVVL system, wherein the fault indicates a differential valve lift condition of the DVVL system. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a functional block diagram of an exemplary six-cylinder engine including a discrete variable valve lift (DVVL) system according to the present disclosure; 
         FIG. 2  illustrates a plot of air-fuel mixture motion of a cylinder with an equivalent intake valve lift and a cylinder with a differential intake valve lift; 
         FIG. 3A  illustrates a plot of normalized cylinder pressure versus crank angle of an exemplary six cylinder engine operating in a high lift (HL) mode and a corresponding knock signal; 
         FIG. 3B  illustrates a plot of normalized cylinder pressure versus crank angle of an exemplary six cylinder engine in an HL mode with one cylinder experiencing a differential intake valve lift and a corresponding knock signal; 
         FIG. 4  is a functional block diagram of DVVL diagnostic control module according to the present disclosure; and 
         FIG. 5  is a flowchart illustrating exemplary steps executed to determine a valve lift malfunction for the DVVL engine system. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     According to the present disclosure, a discrete variable valve lift (DVVL) diagnostic control system limits engine speed if a DVVL engine system is deemed to be malfunctioning. More specifically, a malfunction may occur when intake and/or exhaust valve operation is not synchronous. For example, a cylinder may include an intake valve operating in a low lift (LL) mode and another intake valve operating in a high lift (HL) mode. This may increase the propensity for knock in the particular cylinder. The DVVL diagnostic control system may determine non-synchronous valve operation based on increased knock. 
     Referring now to  FIG. 1 , a DVVL engine system  10  includes an engine  12  that combusts an air/fuel mixture to produce drive torque. Air is drawn into an intake manifold  14  through a throttle  16 . The throttle  16  regulates air flow into the intake manifold  14 . Air within the intake manifold  14  is distributed into cylinders  18 . Although six cylinders are illustrated, it can be appreciated that the engine  12  may include additional or fewer cylinders  18 . For example, engines having 2, 3, 4, 5, 8, 10 and 12 cylinders are contemplated. A fuel injector (not shown) injects fuel that is combined with air to provide a combustion mixture within the cylinder  18 . A fuel injection system (not shown) regulates the fuel injector to provide a desired air-to-fuel ratio within each cylinder  18 . 
     According to an exemplary embodiment of the present disclosure, the cylinder  18  includes two intake valves and two exhaust valves. First and second intake valves  20 ,  21  selectively open and close to enable the air/fuel mixture to enter the cylinder  18 . The intake valve positions are regulated by intake cam shafts  24 . First and second exhaust valves  26 ,  27  selectively open and close to enable the exhaust to exit the cylinder  18 . The exhaust valve positions are regulated by exhaust cam shafts  32 . Although two intake valves  20 ,  21  and two exhaust valves  26 ,  27  per cylinder  18  are shown, a single intake valve and a single exhaust valve per cylinder  18 , or more than two intake valves and more than two exhaust valves per cylinder may be used in an alternate configuration of the cylinder  18 . 
     A piston (not shown) compresses the air/fuel mixture within the cylinder  18 . A spark plug  34  initiates combustion of the air/fuel mixture which drives the piston in the cylinder  18 . The piston drives a crankshaft (not shown) to produce drive torque. The crankshaft rotatably drives camshafts  24 ,  32  using a timing chain (not shown) to regulate the timing of intake and exhaust valves  20 ,  21 ,  26 ,  27 . Although dual intake camshafts and dual exhaust camshafts are shown, it is appreciated that a single intake camshaft and a single exhaust camshaft may be used in straight line cylinder configuration. 
     The engine  12  may include intake cam phasers  36  and exhaust cam phasers  38  that adjust the rotational timing of the intake and exhaust cam shafts  24 ,  32 , respectively. More specifically, a phase angle of the intake and exhaust cam phasers  36 ,  38  may be retarded or advanced to adjust the rotational timing of the input and output camshafts  24 ,  32 . 
     A knock sensor  40  detects engine knock and outputs a knock signal  42 , which represents the mechanical vibration of the engine  12  in the form of a voltage. Engine knock is defined as an audible knocking sound caused by energy released due to auto-ignition. More specifically, auto-ignition is caused when pressure and/or temperature of the air-fuel mixture within the cylinder are high enough to prematurely induce combustion. According to the present disclosure, engine knock is deemed present when the knock signal  42  exceeds a predetermined threshold level. The threshold level may be an audible level that is measured in decibels. 
     An engine speed sensor  44  generates an engine speed signal  45  indicating the revolutions per minute (RPM) of the engine  12 . An ambient temperature sensor  46  generates a temperature signal  47  indicating the air temperature. A manifold absolute pressure (MAP) sensor  48  generates a MAP signal  49  indicating the pressure within the intake manifold  14 . A mass air flow (MAF) sensor  50  generates a MAF signal  51  indicating the amount of air that flows into the engine  12 . A discrete variable valve lift (DVVL) diagnostic module  52  determines a valve operation malfunction in the DVVL engine system  10 . 
     Referring now to  FIG. 2 , a plot  60  illustrates the motion of the air-fuel mixture during an equivalent intake valve lift and during a differential intake valve lift within a cylinder. More specifically, the motion of the air-fuel mixture is provided in terms of a swirl ratio, which may be defined as the ratio between the angular momentum of the air-fuel mixture to the crankshaft&#39;s angular rotational speed. An equivalent valve lift occurs when both intake and/or exhaust valves within a cylinder operate in the same lift modes. A differential valve lift is when both intake and/or exhaust valves within a cylinder operate in different lift modes. For example, a differential valve lift condition exists when one of the cylinders  18  includes intake valve  20  operating in an HL mode and intake valve  21  is operating in an LL mode. 
     The plot  60  illustrates a greater swirl ratio for a differential valve lift condition versus an equivalent valve lift condition after approximately an exemplary 0.15 valve lift to valve diameter ratio represented by a dotted line  62 . A greater swirl ratio results in increased temperature and pressure within the cylinder, which results in a greater propensity for engine knock. Since a cylinder with a differential valve lift has a higher swirl ratio than a cylinder with an equivalent valve lift, the cylinder with a differential valve lift will have a greater propensity for engine knock. 
     Referring now to  FIG. 3A , a graph  64  illustrates a normalized cylinder pressure trace of the exemplary six cylinder engine  12  in an HL mode and a corresponding knock signal  66 . A plurality of pressure signals  68  are shown for the cylinders  18 . A pressure signal  70 , highlighted in bold, represents a particular cylinders  18  (e.g., cylinder #6 in the firing order). The knock signal  66  indicates small levels of background noise and/or small levels of knock activity. These small levels of knock activity do not create audible knock and occur during normal engine operating conditions. 
     Referring now to  FIG. 3B , an exemplary graph  72  illustrates a normalized cylinder pressure trace of the engine  12  operating in the HL mode with one of the cylinders  18  operating with a differential intake valve lift. More specifically, one of the cylinders  18  includes the intake valve  20  operating in the HL mode and the intake valve  21  operating in the LL mode. A plurality of pressure signals  76  are shown for the cylinders  18 . A pressure signal  78 , highlighted in bold, represents a particular cylinder  18  (e.g., cylinder #6 in the firing order) with a differential intake valve lift. The pressure signal  78  has increased in magnitude as compared to the corresponding pressure signal  70  in  FIG. 3A . This increase in magnitude is the result of the differential intake valve lift. A corresponding knock signal  80  indicates periodic engine knock activity in accordance with the cylinder experiencing differential valve lift. Although the plot  72  indicates that an increase in engine knock activity occurs when an LL failure exists during the HL mode, a similar increase in engine knock activity may be indicated when an HL failure exists during the LL mode. 
     Referring now to  FIG. 4 , the DVVL diagnostic module  52  includes an engine knock threshold module  80 , an analysis module  82  and a limiting module  84 . The engine knock threshold module  80  determines an engine knock threshold. More specifically, if the magnitude of the knock signal  42  is greater than the engine knock threshold, the engine  12  is experiencing engine knock. The engine knock threshold module  80  determines the engine knock threshold based on the environmental conditions and engine operating conditions. More specifically, the engine knock threshold module  80  determines the engine knock threshold based on, but is not limited to, an RPM signal  45 , a MAP signal  49 , an engine speed signal  45 , an ambient temperature signal  47  and a MAF signal  51 . The engine knock threshold module  80  outputs an engine knock threshold signal  86 , which represents the engine knock threshold value. 
     The analysis module  82  analyzes the knock signal  42 . More specifically, the analysis module  82  receives the engine knock threshold signal  86  and uses a engine knock detection algorithm to determine whether the knock signal  42  periodically exceeds the engine knock threshold value. When the knock signal  42  periodically exceeds the engine knock threshold value, it assures that the engine knock is due to a differential valve lift in one or more cylinders  18 . Additionally, the engine knock detection algorithm may be able to determine the specific location of the engine knock. One such engine knock detection algorithm is disclosed in U.S. Pat. No. 6,649,924, which issued on Nov. 18, 2003 and is entitled Optoelectronic Measuring Device, the disclosure of which is incorporated herein by reference in its entirety. It is appreciated that other similar engine knock detection algorithms may be used. The analysis module  82  outputs a valve lift malfunction signal  88  when a periodic engine knock is detected. The limiting module  84  limits the engine speed when periodic engine knock is detected to prevent engine damage. 
     Referring now to  FIG. 5 , exemplary steps executed by the DVVL diagnostic control system will be described in detail. In step  500 , control sets a variable N equal to 1. N is the current cylinder in the firing order that is being monitored. In step  502 , control determines the knock threshold level based on engine operating conditions. In step  504 , control receives the knock signal  42  corresponding to cylinder N. Control analyzes the mean cycle knock activity in step  506 . More specifically, control analyzes the mean knock activity of the particular cylinder N over a plurality of past engine cycles and the current engine cycle. 
     In step  508 , control determines whether knock is present, which corresponds to cylinder N. If knock is not present, control continues in step  510 . If knock is present, control continues in step  512 . In step  510 , control determines whether N is equal to a total number of cylinders in the engine (N TOT ). If N is not equal to N TOT , control increments N in step  514  and loops back to step  502 . If N is equal to N TOT , control loops back to step  500 . In step  512 , control generates a fault signal for cylinder N. In step  516 , control limits the engine speed and control ends. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.