Abstract:
The present invention related generally to a method for determining spark plug malfunction and more particularly to a method for determining spark plug malfunction in an internal combustion engine in which at least two spark plugs are disposed in each cylinder. In a dual plug configuration, a spark plug malfunction is detected by disabling one of the spark plugs during a test period in a particular cylinder. A misfire provides an indication of malfunction of the other spark plug.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a method for determining spark plug malfunction. 
     2. Background of the Invention 
     To ensure engine emission performance, it is desirable to perform testing of the engine during operation. An engine equipped with two spark plugs per cylinder provides a unique opportunity to detect a spark plug failure. According to U.S. Pat. No. 5,872,312, one of the two spark plugs in each cylinder in a bank of the engine&#39;s cylinders is disabled. Stated another way, one half of the spark plugs in an entire bank are simultaneously disabled. If a misfire is detected during testing on the bank of cylinders, a spark plug of each cylinder is disabled in succession. In this way, it may be determined which spark plug is experiencing a malfunction. 
     The inventors have recognized a problem with the approach in U.S. Pat. No. 5,872,312 in that, if a spark plug is malfunctioning, two misfires occur in the process of identifying the malfunctioning cylinder, i.e., a first misfire occurs in the bank testing of cylinders and a second misfire in testing individual cylinders. Because a misfire may lead to hydrocarbon emission and may cause overheating of an exhaust catalyst, misfire occurrence should be minimized. The inventors of the present invention have recognized an alternative procedure to detect spark plug malfunction which overcomes the problem of multiple misfires. 
     SUMMARY OF INVENTION 
     Disadvantages of prior art approaches are overcome by a method for controlling and diagnosing a multi-cylinder internal combustion engine having two spark plug in each cylinder to determine spark plug malfunction by disabling one of the spark plugs during a test period in a particular cylinder. It is determined whether a misfire has occurred during the disablement, which provides an indication of malfunction of the other spark plug. During the test period, each spark plug is disabled only once. 
     An advantage of the present invention is that if a spark plug malfunction is occurring, it can be detected in one misfire occurrence. In prior art, two misfires occur in performing the detection scheme. Because misfires lead to short bursts of higher exhaust emissions and a large increase in catalyst temperature, the present invention provides a clear advantage in lower hydrocarbon emission and a lower potential for overheating and possibly melting a catalyst. 
     An additional advantage is that the present invention requires fewer processes to be undertaken to determine which spark plug is malfunctioning. The algorithm may be performed in a shorter period of time, thereby providing a more rapid identification of a malfunctioning spark plug. 
     According to another aspect of the present invention, a method for controlling and diagnosing a multi-cylinder internal combustion engine is disclosed in which an ignition spark is provided through a first spark plug positioned in one of the cylinders near a center axis of the cylinder and ignition spark is provided through a second spark plug positioned in the cylinder near a wall of the cylinder. The first spark plug is disabled during a test period in one of the cylinders and it is determined whether a misfire has occurred during the period that the first spark plug is disabled. A misfire provides an indication of a malfunction of the second spark plug. An advantage of this aspect of the present invention in providing smoother engine operation during the diagnostic procedure than prior art methods in engines with one of the spark plugs located near a cylinder wall and one of the spark plugs centrally located. When prior art approaches are used to diagnose the spark plugs located near a wall in a dual bank engine, the centrally located plug along an entire bank of cylinders are disabled simultaneously. Even if none of the spark plugs being diagnosed were malfunctioning, simply by performing the diagnostic procedure torque drops about 15% during the disablement due to the loss of combustion initiation in the dominant position, the central position. Such a torque drop would be noticeable and objectionable to the driver. The situation is even worse if the prior art diagnostic routine were performed on an engine with a single bank of cylinders. The present invention, in contrast, provides for diagnosing one cylinder at a time resulting in a torque loss of about 5% (in a 6-cylinder engine), which is well within the range of normal cycle-to-cycle torque differences. 
     The above advantages, other advantages, and other features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The advantages described herein will be more fully understood by reading an example of an embodiment in which the invention is used to advantage, referred to herein as the Detailed Description, with reference to the drawings wherein: 
     FIG. 1 is a schematic of a V-6 engine with two spark plugs per cylinder; 
     FIG. 2 is a cross-sectional representation of the valves and spark plugs as they may be arranged in a single cylinder of the engine; 
     FIG. 3 is a cross-sectional representation of the valves and spark plugs as they may be arranged in a single cylinder of the engine; and 
     FIG. 4 is a flowchart indicating steps by which the present invention may be used to advantage. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1 a six-cylinder engine  10  is shown. Engine  10  contains two banks,  12  and  14 , of cylinders with three cylinders in each bank. The present invention applies to any number of engine banks with any number of cylinders per bank. Each cylinder  16  contains two spark plugs  18 . However, the present invention also applies to more than two spark plugs per cylinder. Spark plugs  18  may be arranged in various configurations in the cylinder and will be discussed more fully below in regards to FIGS. 2 and 3. Spark plugs  18  are connected to ignition coils  52 , shown for one cylinder only in FIG.  1 . The configuration shown in FIG. 1 is commonly called coil on plug. The present invention also applies to other coil configurations. Ignition coils  52  are connected to battery  50 , which supplies battery voltage to the low voltage side of ignition coil  52 . Ignition coil  52  transforms low voltage to high voltage, which is provided to spark plugs  18 . Ignition coils  52  are controlled or switched by coil driver  60 , which is shown on board electronic control unit  40  (ECU) in FIG.  1 . However, coil driver  60  may be mounted elsewhere and provide the same function. A signal is supplied by spark controller  62  to cause coil driver  60  to switch, thereby causing spark firing. 
     Various devices may be used to assess whether combustion occurs in response to a request for spark plug firing. Engine  10  has a toothed disk  20  coupled to the crankshaft (not shown) of engine  10 . Sensor  22  provides an output as the teeth of toothed disk  20  pass by sensor  22 . Engine speed can be computed based on the signal from teeth passing sensor  22 . Engine speed drops momentarily when a cylinder experiences a misfire, i.e., combustion failure. Alternatively, a misfire is detected by an engine sensor  24  as shown in FIG. 1, by way of example, in one cylinder of engine  10 . However, each cylinder  16  of engine  10  preferably would contain engine sensor  24 . Engine sensor  24  may be a luminosity detector which senses the light in the cylinder entering the detector. As combustion emits visible light, detection of light can be used to indicate whether combustion has been initiated. Alternatively, engine sensor  24  may be a pressure sensor. Cylinder pressure increases due to a combustion event; thus, pressure may also be used to determine whether combustion has been initiated. Engine block sensor  26  may be a strain gauge attached to the surface of the engine block, the output of which is affected by the pressure developed in cylinders  16 . In FIG. 1, only one engine block sensor  26  is shown. It may be found that multiple engine block sensors  26  are needed to accurately determine whether a combustion event has occurred. 
     A piston (not shown) is disposed and reciprocates within each cylinder  16  of engine  10 . In four-stroke operation, the processes are: an intake stroke during which the piston moves down or away from the cylinder head (not shown) in which the spark plugs  18  are typically disposed, a compression stroke as the piston moves up, an expansion or power stroke as the piston moves down, and an exhaust stroke as the piston moves up. Combustion typically is initiated toward the end of the compression stroke with the majority of combustion occurring during the expansion stroke. If spark plugs  18  fail to ignite the fuel and air mixture in a particular cylinder, the mixture does not combust and the expansion stroke provides much less power to the engine&#39;s crankshaft than if a combustion event had occurred. The rotational speed of engine  10  dips slightly when combustion in one of the cylinders fails to occur. The drop in speed, however, is momentary and occur only during part of a revolution of engine  10  because the next cylinder to undergo an expansion stroke produces power causing engine  10  to reattain the speed prior to misfire. Other known methods of detecting engine misfire which may be used to advantage include: detecting an anomalous signal from an gas sensor (not shown) positioned in the engine exhaust which measures exhaust air/fuel ratio and detecting changes in alternator (not shown). 
     ECU  40  is provided to control engine  10 , in general, and spark plugs  18 , as shown specifically in FIG.  1 . ECU  40  has a microprocessor  72 , called a central processing unit (CPU), in communication with memory management unit (MMU)  74 . MMU  74  controls the movement of data among the various computer readable storage media and communicates data to and from CPU  72 . The computer readable storage media preferably include volatile and nonvolatile storage in read-only memory (ROM)  76 , random-access memory (RAM)  80 , and keep-alive memory (KAM)  78 , for example. KAM  78  may be used to store various operating variables while CPU  72  is powered down. The computer-readable storage media may be implemented using any of a number of known memory devices such as PROMs (programmable read-only memory), EPROMs (electrically PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electric, magnetic, optical, or combination memory devices capable of storing data, some of which represent executable instructions, used by CPU  72  in controlling the engine or vehicle into which the engine is mounted. The computer-readable storage media may also include floppy disks, CD-ROMs, hard disks, and the like. CPU  72  communicates with various sensors and actuators via an input/output (I/O) interface  70 . Examples of items that are actuated under control by CPU  72 , through I/O interface  70 , are fuel injection timing, fuel injection rate, fuel injection duration, throttle valve position, spark plug timing, and others. Sensors  42  communicating input through I/O interface  70  may be indicating engine rotational speed  22 , vehicle speed, coolant temperature, manifold pressure, pedal position, throttle valve position, air temperature, exhaust temperature, and air flow  50 . Spark plug timing is determined in CPU  62  and communicated to spark controller  62 . This configuration of spark controller  62  comprising a separate chip in FIG. 1 is shown by way of example. Alternatively, the functionality of spark controller  62  could be contained in CPU  72 . Some ECU  40  architectures do not contain MMU  74 . If no MMU  74  is employed, CPU  72  manages data and connects directly to ROM  76 , RAM  80 , and KAM  78 . Of course, the present invention could utilize more than one CPU  72  to provide engine control and ECU  40  may contain multiple ROM  76 , RAM  80 , and KAM  78  coupled to MMU  74  or CPU  74  depending upon the particular application. 
     In FIG. 2, an example of a two spark plug  18  arrangement is shown for one cylinder in which one spark plug  18  is centrally located and one spark plug  18  is located near the periphery of the cylinder  16 , near the cylinder  16  wall. In this case, the central plug may be considered a primary plug and the peripheral plug a secondary plug. The primary initiates the primary combustion event; and the secondary plug assists with later combustion or may provide additional certainty of combustion under marginal circumstances, such as cold start, high dilution of the combustion gases with burned gases, or lean burn. Also shown in FIG. 2, by way of example, are two exhaust valves  30  and an intake valve  32 . Another alternative is shown in FIG. 3, in which both spark plugs  18  are located near a cylinder  16  wall. In this case, both plugs provide substantially similar combustion waves, i.e., neither is considered a dominant plug. Regardless of spark plug  16  configuration and their relative importance in initiating combustion, the present invention may be applied to any multiple plug configuration. Also, the exhaust valves  30  and intake valve  32  configuration shown in FIGS. 2 and 3 is merely illustrative and the present invention applies to any arrangement, combination, and number of intake and exhaust valves. 
     Referring now to FIG. 4, a diagnostic procedure for detecting a spark plug malfunction begins in step  82 . The diagnostic procedure of the present invention depends on there not being a misfire, possibly due to a cause other than a spark plug malfunction such as low compression in a cylinder or a fuel injector problem. Thus, before getting to the heart of the detection scheme in which various spark plugs are temporarily disabled, it is determined if there is a misfire occurring in step  83 . If there is a misfire occurring (positive result in step  83 ), the diagnostic procedure is discontinued by proceeding directly to step  100 . If there is no misfire, i.e., a negative result in step  83 , control passes to step  84 , in which counters i and j are initialized to 1. Counter i is the cylinder number on the bank and j is the number of the bank. Control passes to step  86  in which one of the ij spark plugs are disabled. The testing may commence on the primary spark plug of each cylinder of the secondary spark plug in each cylinder. Alternately, these could be termed first and second spark plugs. If the primary spark plug is the subject of the diagnostic procedure, the secondary spark plug is the one that is disabled. The discussion below assumes the diagnostic procedure is being performed on the primary spark plug in each cylinder. In step  88  it is determined if the engine experienced a misfire during the time of disablement of the secondary spark plug in the ij cylinder. If a positive result in step  88 , control passes to step  90  in which a flag is set in ECU  40  indicating that the primary spark plug in the ij cylinder misfired. Control then passes to step  91 ; similarly control passes to step  91  if a negative result is returned in step  88 . Regardless, in step  91  the secondary spark plug in the ij cylinder is enabled. Control then passes to step  94  where it is determined whether i=m. In the example of the V-6 engine, the number of cylinders per bank is 3; thus, m is 3, and the number of banks is 2; thus, n is 2. The diagnostic procedure is set up to assess all of the cylinders by counting i=1 through 3 and j=1 through 2, through all combinations. If a negative result is returned in step  94 , control passes to step  98  where counter i is incremented and control passes back to step  86  where the secondary spark plug in the new ij cylinder is disabled for assessment of the primary plug. If a positive result is returned in step  94 , this indicates that all of the cylinders on the jth bank have been assessed and control passes to step  96  in which it is determined whether j is equal to n. If a positive result is returned in step  96 , the diagnostic procedure is terminated in step  100 . If a negative result is returned in step  96 , counter i is reset and counter j is incremented in step  92 . Control then passes to step  86  where the new ij cylinder is assessed. Alternatively, the flowchart in FIG. 2 could be configured such that counter i counts through all the cylinders without regard for banks. Consequently, all references to j and n would be removed; step  94  would proceed directly to step  100 ; and, steps  92  and  96  would be removed. In this case, m would be equal to the total number of cylinders, eg., 6 for engine  10  of FIG.  1 . 
     The procedure described in conjunction with FIG. 4 may be used for a first spark plug in each cylinder and repeated to assess a second spark plug in each cylinder. The present invention may be extended to a cylinder with more than two spark plugs. To assess a malfunction of a particular spark plug in such a configuration, all other spark plugs in that cylinder are disabled briefly to determine if the particular spark plug is malfunctioning. 
     The method for detecting a malfunction of a spark plug in a multiple plug described herein produces a momentary misfire of a cylinder, if a malfunctioning plug exists, an unlikely event. If this unlikely event does occur, no substantial functional disturbance to the engine performance results. Although this causes a slight drop in engine speed, if measured on the time scale of a part of a revolution, it is unnoticeable to the average operator. Instead, a savvy operator may notice the misfire only by aural cues, not by a noticeable drop in engine speed. The misfire causes a discharge of unburned fuel and air from the engine  10 , which reacts in a catalytic converter, if engine  10  is so equipped. Oxidation of fuel in the catalytic converter leads to a large temperature rise in the catalytic converter and may harm the catalytic converter, particularly if several misfire events occur in rapid succession. Thus, although a single misfire event may be tolerated by the engine system, multiple misfire events should be avoided. 
     While several modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize alternative designs and embodiments for practicing the invention. The above-described embodiments are intended to be illustrative of the invention, which may be modified within the scope of the following claims.