Abstract:
A method of providing engine timing information for an engine having a plurality of cylinders including detecting a fault for a crankshaft sensor generating engine timing information with a camshaft sensor, providing spark and fuel with the engine timing information generated by the camshaft sensor, and shutting off fuel to at least one of the cylinders.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to the control of an internal combustion engine. More specifically, the present invention relates to controlling an internal combustion engine upon the failure of a crankshaft position sensor.  
         BACKGROUND OF THE INVENTION  
         [0002]    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 information for a crankshaft and a camshaft is very important to the application and synchronization of spark and fuel. The crankshaft is actuated by combustion in the pistons, and the camshaft actuates the intake and exhaust valves of the pistons. 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.  
           [0003]    In today&#39;s engine control systems, crankshaft speed supplied by a crankshaft sensor provides position, timing, and/or speed information to an electronic controller 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 OHC engine may be controlled relative to the crankshaft (piston position) to reduce emissions and improve fuel economy. Several cam-phasing devices exist in today&#39;s automotive market that require accurate position and timing information provided by a camshaft position sensor.  
           [0004]    A crankshaft or camshaft position sensing system typically includes 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 crankshaft or camshaft. In a four-cycle ICE, the electronic controller must further differentiate the intake, compression, power, and exhaust strokes since the cylinders will be approaching top dead center (TDC) position during the compression and exhaust phases and approaching bottom dead center (BDC) position during the intake and power phases. Accordingly, the application of fuel and spark in a typical ICE will not be applied until enough position information has been obtained from the crank position sensing systems. Thus, the engine controller must not only determine the TDC and BDC positions of the cylinder but also the state of the engine cycle to control fuel and spark. In the event of a failure of the crankshaft position sensor or system, engine timing must somehow be determined to allow a vehicle to function well enough to travel to a destination where the failure can be fixed.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention comprises a method and apparatus to allow a vehicle engine to operate in the event of a crankshaft sensor failure used in sensing systems common to four cycle ICEs, including but not limited to four-, five-, six- and eight-cylinder engines. The camshaft position sensing system of the present invention, specifically the sensor and target wheel used to provide position information for the camshaft and phasing of the camshaft, may be used to provide timing signals for control of fuel and spark in the event of a crankshaft sensor failure.  
           [0006]    The present invention utilizes a 4× target wheel cam with four. binary (state encoded) base periods for engine cam timing functions. Each semi-period or state is bounded by a rising and falling edge that are a fixed angle before TDC for one or more cylinders of all four, five, six, and eight cylinder engine configurations. For five- or six-cylinder engine configurations, a 4× target wheel used in a camshaft sensing system may not provide accurate information on the position of a particular cylinder/piston. If spark is applied too early to a cylinder (the cylinder is over-advanced by 20-30 degrees), a negative torque spike may occur. The negative torque spike can create stress on the crankshaft and be transmitted through the crankshaft to a starter motor. Starter motors are typically mounted by a flange to an engine block and are connected to the crankshaft through a coupling such as a gear box or belt. The negative torque spike created by the mis-timing of fuel and spark to an engine may destroy the starter motor coupling or fracture the engine block.  
           [0007]    The present invention utilizes the 4× target wheel of the camshaft positioning system to provide backup or redundant information to an engine controller for engine timing. Furthermore, for certain engine types such as five-cylinder or six-cylinder engines, the application of spark and fuel for certain cylinders may be prevented to eliminate a negative torque spike. Fuel and spark are supplied to the engine sequentially, one cylinder at a time. When a position within a 720 degree engine cycle is reached where a fuel injector or ignition event for a cylinder can create an over-advance condition, ignition in that cylinder is prevented by turning off the fuel injector and/or spark ignition device. The absence of fuel and spark to that individual cylinder ensures that the cylinder does not produce any torque, positive or negative. All cylinders that cannot generate the over-advance condition are operated with normal fuel injection and spark events.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    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:  
         [0009]    [0009]FIG. 1 is a diagrammatic drawing of the engine and cam sensing system of the present invention;  
         [0010]    [0010]FIG. 2 is a diagrammatic drawing of a 4× target wheel used for camshaft position sensing in the present invention; and  
         [0011]    [0011]FIGS. 3A, 3B and  3 C are timing diagrams illustrating the signals generated by the position sensing systems of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]    [0012]FIG. 1 illustrates an internal combustion engine  10  having a crankshaft  12 . The speed of the crankshaft  12  is communicated in the form of periodic signals generated by the rotation of a target wheel  15  on the crankshaft  12  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 a 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 periodic signals generated by the speed sensor  16 .  
         [0013]    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 . In the preferred embodiment of the present invention, the fuel injectors are configured as port injectors where each cylinder is supplied with fuel from a fuel injector. The controller  22  further includes calibration constants and software stored in NVM  26  that may be applied to control numerous engine types.  
         [0014]    In the preferred embodiment of the present invention, as shown in FIG. 1, the engine  10  is shown with exhaust camshaft  14  and intake camshaft  19 . The exhaust camshaft  14  and intake camshaft  19  are coupled to the crankshaft  12  via sprockets and a timing chain  25 . 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 position sensor  18  to provide speed and position information for the exhaust camshaft  14 . The wheel position sensor  18  may be similar in functionality to wheel speed sensor  16 .  
         [0015]    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 may be coupled to the exhaust camshaft  14 . In alternate embodiments of the present invention, a cam phaser  32  may be coupled to the intake camshaft  19  or to both the exhaust and intake camshafts  14 ,  19 , depending on the desired performance and emission requirements of the engine  10 . The cam phaser  32  is hydraulically modulated to create a variable rotational offset between the exhaust camshaft  14  and the intake camshaft  19 . The degrees 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 engine  10 .  
         [0016]    [0016]FIG. 2 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 diagrams of FIGS. 3A, 3B and  3 C. The target wheel  23  includes an irregular surface having teeth, slots, or tabs  40 . The teeth  40  have edges E 1 -E 8  for generating a pulse train for the wheel position sensor  18 .  
         [0017]    Referring to FIGS. 3A, 3B and  3 C, a timing diagram is shown with a series of exhaust, intake and ignition events, a pulse train  52  generated by the target wheel  15  and target wheel sensor  16 , and pulse trains  54  generated by the target wheel  23  and target wheel position sensor  18 . Plot  54   a  corresponds to timing events for a four-cylinder engine, plot  54   b  corresponds to timing events for a five-cylinder engine, plot  54   c  corresponds to timing events for a six-cylinder engine, and plot  54   d  corresponds to timing events for an eight-cylinder engine. The pulse train  54  includes edges E 1 -E 8  that correspond to the physical layout of the teeth  40  on target wheel  23 . The edges E 1 -E 8  signal the controller  22  the position and speed of the exhaust camshaft  14  and the state of the crankshaft  12  (i.e., is it in the compression or exhaust phase) and corresponding cylinders to allow the application of spark and fuel by the controller  22  in the case of a failure of target wheel sensor  16  for the crankshaft  12 .  
         [0018]    During the operation of an engine such as a five- or six-cylinder engine, the crankshaft target wheel sensor  16  may fail or other failures may occur that prevent timing information to be recorded from the target wheel sensor  16 . In such cases, the vehicle may operate using the camshaft target wheel  23  and position sensor  18 . The position information provided by the position sensor  18  can be used to determine the application of fuel and spark to the engine  10 . A 4× target wheel such as target wheel  23  in certain situation may not provide reliable position and timing information for the engine  10 . Referring to FIGS. 3A, 3B and  3 C, plot  54   b  and edges E 6 , E 8 , El, E 2  and E 5  will be used to provide crankshaft position information. Cylinders A, B, C, D and E for a five-cylinder engine can be referenced in plot  54   b  for a five-cylinder engine.  
         [0019]    In the preferred embodiment of the present invention, the edges E 6 , E 8 , El, E 2 , and E 5  for a five-cylinder engine produce a signal thirty-six degrees from the TDC position for cylinder A, zero degrees from the TDC position for cylinder B, twelve degrees after the TDC position for cylinder C, one hundred-eight degrees from the TDC position for cylinder D, and forty-eight degrees from the TDC position for cylinder E. If the speed can be predicted correctly, accurate firing of spark and the application of fuel can be done with reference to the edges E 6 , E 8 , E 1 , E 2 , and E 5 . In certain operating conditions for the cylinder D, the engine  10  may slow down, as shown by the plot  52  in FIG. 3C. The predicted position  50  and actual position  52  of the piston may be inaccurate. The piston could be in an over-advanced position where negative torque will be generated by spark and fuel. In such a situation, spark and/or fuel may be cut off to that particular cylinder to prevent the negative torque spike.  
         [0020]    When E 2  is reached, this would be the normal event to turn on a fuel injector or set up a ignition event for cylinder D. However, since ignition at this event can cause an over-advance condition, cylinder D ignition is prevented by turning off the fuel injector and/or spark ignition device. The absence of fuel and spark to cylinder D ensures it does not produce any torque, positive or negative  
         [0021]    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.