Abstract:
A camshaft system for use with an internal combustion engine including a camshaft having a plurality of lobes to actuate valves in the internal combustion engine, a sprocket coupled to the camshaft to drive the camshaft, and a target wheel coupled to the camshaft, the target wheel having an irregular surface capable of providing process data for operation of a plurality of internal combustion engine configurations.

Description:
TECHNICAL FIELD 
     The present invention relates to the control of an internal combustion engine. More specifically, the present invention relates to a global cam sensing system that may be integrated seamlessly with multiple internal combustion engines having a plurality of cylinder configurations. 
     BACKGROUND OF THE INVENTION 
     Integration of vehicle parts, electronic components, and software into automotive vehicles is becoming increasingly important in today&#39;s automotive industry. Traditional methods of vehicle assembly for vehicle parts and components is giving way to flexible modular design and manufacturing techniques. 
     Presently, automotive companies manufacture a wide range of internal combustion engine (ICE) configurations such as in-line four-cylinder engines, in-line five-cylinder engines, in-line six-cylinder engines, and V-eight engines. As is known in the art of four-cycle ICEs, position and timing between a crankshaft and a camshaft is very important for the application and synchronization of spark and fuel, as the camshaft actuates the intake and exhaust valves of an ICE. 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. 
     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 overhead cam 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. The camshaft position sensor 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 camshaft. 
     The target wheel or data wheel used in present camshaft position sensors has a generally regular distribution of teeth, tabs, and/or slots. In a four cycle ICE, the electronic controller must further differentiate the intake, compression, power, and exhaust strokes since the cylinders will be at the top dead center (TDC) position during the compression and exhaust phases and at the 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 or cam 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. 
     Target or data wheels for a camshaft that provide camshaft position may either be common across all engine configurations (i.e., the number of cylinders) or specific for each engine configuration. Target wheels that are designed to be specific to the number of cylinders in the engine provide the optimum data for functions such as control of a camshaft phaser or delivery of fuel/spark in the event of a failure of the crank sensor circuit. These present systems have the disadvantages of requiring different hardware and software for each engine configuration. Target wheels that are common across all engine configurations may provide the advantage of faster engine position information, but lack enough position information for optimum control of a cam phaser and delivery of fuel/spark in the event of a failure of the crankshaft sensor system. It would be advantageous for an automotive company to utilize a single type of generic camshaft sensing system with a single generic target wheel and calibratible software that can be used on a plurality of engine configurations, while still providing for control of cam phasers, and delivery of fuel/spark in the event of a failure of the crank sensor system, and providing the fastest engine position information. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a new camshaft sensing system common to four cycle internal combustion engines (ICEs), including but not limited to four, five, six, and eight cylinder engines. The cam system, and specifically the sensor and target wheel, provide an output signal with “events” at a fixed location relative to top dead center (TDC) compression for cylinders of the engine configurations listed above. This is achieved with the minimum number of sensing features possible to reduce the cost, complexity, and control system throughput of the camshaft sensing system, while maximizing functionality and providing quick engine synchronization. 
     The present invention utilizes an 8×+s cam with eight 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. In the present invention, the edge that corresponds to TDC for cylinder one is common to all engine configurations. In addition to the base periods for engine timing functions, an additional state is added to the system at a location known as the synchronization region or pulse. This state and its bounding edges are used purely to synchronize the engine quickly when the crank position has been determined. The common camshaft sensing system of the present invention can be used on a plurality of engine types with no loss of functionality, as compared to cylinder number specific cam systems or 1× cam system of the prior art. 
     The 8×+s cam sensing system of the present invention places an edge (electrical signal) at a consistent location prior to TDC for all four, five, six and eight cylinder engine configurations. Through programming and calibration, each engine controller selects which edge numbers it will use for specific cam tasks. These will generally be those edges that fall at a consistent angle prior to TDC for the specific engine configuration. In addition, all engines will use the ½ period known as the sync pulse, and the corresponding opposite state of the cam signal 360 crank degrees later to achieve the full engine sync as quickly as possible. The combination of these properties is unique to this cam sensing system and provides the ability to do all known cam tasks with the highest degree of accuracy using a single common cam system. 
     The camshaft sensing system of the present invention provides cost, assembly, and integration benefits, as compared to existing cylinder specific cam systems. In addition, the camshaft sensing system of the present invention provides increased functionality over existing systems by providing engine cycle position and timing, cylinder event based cam control (for cam phaser applications), and a backup speed and position signal for spark and fuel control in the event of a failure of the crankshaft sensor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a diagrammatic drawing of the engine and cam sensing system of the present invention; 
     FIG. 2 is a perspective drawing of the engine used in the preferred embodiment of the present invention; 
     FIG. 3 is a diagram of the preferred embodiment of a target wheel used in the present invention; and 
     FIG. 4 is a timing diagram illustrating the signals generated by the target wheel of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, an internal combustion engine  10  having a crankshaft  12  communicates 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 . 
     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 . The controller  22  further includes calibration constants and software stored in NVM  26  that may be applied to control numerous engine types. 
     In the preferred embodiment of the present invention, as shown in FIG. 2, an inline six-cylinder engine 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  20  and  21  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 . 
     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 ICE  10 . The cam phaser  32  is hydraulically modulated to create a variable rotational offset between the exhaust camshaft  14  and the intake camshaft  19  and/or the crankshaft  12 . 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 ICE  10 . In applications where it is required that NOx components are reduced, the cam phaser  32  can provide charge dilution in the form of recirculated exhaust gases. Charge dilution is a method of adding an inert substance to the air/fuel mixture in a cylinder of the ICE  10 . The inert substance will increase the heat capacity of the air/fuel mixture and reduce the amount of NOx components created during combustion. Thus, by regulating the valve overlap area, NOx components may also be regulated. Furthermore, engine performance characteristics such as horsepower and fuel economy may also be modified using the cam phaser. 
     FIG. 3 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 diagram of FIG.  4 . The target wheel  23  includes an irregular surface having teeth, slots or tabs  40 . The teeth  40  have edges E 1 -E 18  for generating a pulse train for wheel position sensor  18 . Referring to FIGS. 4A-4C, a timing diagram is shown with a series of exhaust, intake and ignition events  50 , a pulse train  52  generated by the target wheel  15  and target wheel sensor  16 , and a pulse train  54  generated by the target wheel  23  and target wheel position sensor  18 . The pulse train  54  includes edges E 1 -E 18  that correspond to the physical layout of the teeth  40  on target wheel  23 . The edges E 1 -E 18  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 . 
     Lines A-P in FIGS. 4A-4C correspond to the top dead center (TDC) position in time for the various engine configurations that may be used with the target wheel  23  of the present invention such as four, five, six and eight cylinder engines. Referring to FIGS. 4A-4C, line A indicates the TDC position for cylinder one of a four, five, six and eight cylinder engine. Line B indicates the TDC position for cylinder two of an eight-cylinder engine, Line C indicates the TDC position for cylinder two of a six-cylinder engine. Line D indicates the TDC position for cylinder two of a five-cylinder engine. Line E indicates the TDC position for cylinder three of an eight-cylinder engine and cylinder two of a four-cylinder engine. Line F indicates the TDC position for cylinder three of a six-cylinder engine. Line G indicates the TDC position for cylinder four of an eight-cylinder engine. Line H indicates the TDC position for cylinder three of a five-cylinder engine. Line I indicates the TDC position for cylinder five of an eight-cylinder engine, cylinder four of a six-cylinder engine and cylinder three of a four-cylinder engine. Line J indicates the TDC position for cylinder four of a five-cylinder engine. Line K indicates the TDC position for cylinder six of an eight-cylinder engine. Line L indicates the TDC position for cylinder five of a six-cylinder engine. Line M indicates the TDC position for cylinder seven of an eight-cylinder engine and cylinder four of a four-cylinder engine. Line N indicates the TDC position for cylinder five of a five-cylinder engine. Line  0  indicates the TDC position for cylinder six of a six-cylinder engine. Line P indicates the TDC position for cylinder eight of an eight-cylinder engine. 
     As can be seen in the timing diagram of FIG. 4, lines A-P generally correspond in time to the edges E 1 -E 16  of the pulse train  54  generated by the target wheel  23 . A synchronization pulse  58  generated by the crankshaft  12  signals the control system to read the state of the cam sensor  18  input. This is generally done when the camshaft is in its rest position. The state will be low if the cam sensor  18  is in the sync region (between E 17  and E 18 ) or high if the camshaft is between edges E 8  and E 9 . A synchronization pulse  56  generated by edges E 17  and E 18  of target wheel  23  enables the control system to instantly determine if cylinder one is in a compression or exhaust state. 
     The target wheel  23  of the present invention may be used on a plurality of engines having multiple cylinder configurations. This aids in manufacturing and assembly of an engine since only one control system will need to be produced as opposed to multiple control systems. A vehicle equipped with a specific engine configuration need only be calibrated to reference the edges E 1 -E 16  that correspond to the specific engine configuration. In the preferred embodiment of the present invention, the electronic controller  22  contains software in NVM  26  to operate any type of engine configuration and a flag is set to signal the controller  22  what type of engine it will be controlling. 
     The control system of the present invention further provides cam phase measurement to provide feedback to the controller  22  as it modulates the cam phaser  26 . The target wheel  23  and associated position sensor  18  also provides a redundant engine signal to determine if the crank speed sensor  16  is performing correctly. If the crank speed sensor  16  has failed, the position sensor  18  will provide engine speed and position information to the controller  22 , enabling the controller  22  to schedule fuel and spark in the event of the loss of the crank sensor. The cam phaser measurement and the application of fuel and spark may be used by the present invention for any ICE configuration by using the edges E 1 -E 16  that are specified in software for a particular engine configuration. 
     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.