Abstract:
A reverse rotation detection system for an engine with at least one camshaft and a crankshaft includes a camshaft position sensor that generates a camshaft position signal based on a rotation of the camshaft. A second sensor input device generates a crankshaft position signal based on a rotation of the crankshaft. A control module detects a reverse rotation condition of the engine from the camshaft position signal and the crankshaft position signal, wherein the control module compares the camshaft position signal to the crankshaft position signal to determine an engine position. Based on the engine position the control module compares the camshaft position signal to an expected signal to determine a reverse rotation condition.

Description:
FIELD OF THE INVENTION 
     The present invention relates to internal combustion engines, and more particularly to systems and methods for detecting continuous reverse rotation of an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     An internal combustion engine generally operates in four modes; an intake mode, a compression mode, a combustion mode and an exhaust mode. During reverse rotation of an engine, the engine cycle executes in a reverse order whereby the compression mode is followed by the intake mode. For example, when an engine that is stopped begins to start again, the engine may have a cylinder that was in a compression mode at the moment of stopping. Compression pressure in the cylinder may push a piston in reverse toward bottom dead center (BDC). When engine speed increases, a cylinder with injected fuel may experience ignition and the reverse rotation may be accelerated. 
     It is unlikely that a conventional engine will rotate in reverse for a long period of time. Torque control systems are capable of limiting the duration of the reverse rotation. However, the problem arises more frequently in hybrid electric propulsion systems. An external force (such as an electric motor) can rotate the internal combustion engine in reverse for longer durations at higher speeds. Conventional torque control systems are not able to control torque under these conditions. 
     If reverse rotation occurs, engine components such as the intake manifold can be damaged. Reverse rotation may cause a compressed air/fuel mixture to flow back into the intake manifold during the intake stroke through an open intake valve. Pressure in the intake manifold increases. If further reverse rotation occurs, pressure may increase further and cause damage to the intake manifold. 
     SUMMARY OF THE INVENTION 
     Accordingly, a reverse rotation detection system for an engine with at least one camshaft and a crankshaft includes a camshaft position sensor that generates a camshaft position signal based on a rotation of the camshaft. A second sensor input device generates a crankshaft position signal based on a rotation of the crankshaft. A control module detects a reverse rotation condition of the engine from the camshaft position signal and the crankshaft position signal, wherein the control module compares the camshaft position signal to the crankshaft position signal to determine an engine position. Based on the engine position the control module compares the camshaft position signal to an expected signal to determine a reverse rotation condition. 
     In one other feature, if the engine position indicates that the camshaft is retarded relative to the crankshaft, the expected signal is selectable for a crankshaft region. The region is defined by a first crankshaft angle and a second crankshaft angle referenced relative to top dead center of a cylinder of the engine. The control module compares an edge of the camshaft position signal to an edge of the expected signal. 
     In other features, if the engine position indicates that the camshaft and the crankshaft are synchronized, the expected signal is the camshaft position signal at a region of the camshaft stored during a previous rotation of the crankshaft. The region is defined by a first camshaft angle and a second camshaft angle. The control module compares a state of the camshaft position signal to a state of the expected signal. 
     In still other features, the system includes a wheel coupled to the camshaft having a plurality of teeth, wherein the camshaft position sensor generates the camshaft sensor signal based on the plurality of teeth of the wheel. The system can also include a wheel coupled to the crankshaft having a plurality of teeth, wherein the crankshaft position sensor generates the crankshaft position signal based on the plurality of teeth of the wheel. 
     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 schematic illustration of the top view of an engine system; 
         FIG. 2  is a schematic illustration of the side view of an engine system; 
         FIG. 3  is a flowchart illustrating steps taken by the engine system to detect a reverse rotation of the engine according to the present invention; and 
         FIG. 4  is a timing diagram illustrating exemplary signals used to detect a reverse rotation of the engine. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment 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, 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. 
     Referring now to  FIG. 1 , an engine system  10  includes an engine  12  that combusts an air and fuel mixture to produce drive torque. Air is drawn into an intake manifold  14  through a throttle  16 . The throttle  16  regulates mass air flow into the intake manifold  14 . Air within the intake manifold  14  is distributed into cylinders  18 . Although four cylinders  18  are illustrated, it can be appreciated that the engine can have a plurality of cylinders including, but not limited to, 2, 3, 5, 6, 8, 10, 12 and 16 cylinders. 
     A fuel injector (not shown) injects fuel that is combined with the air as it is drawn into the cylinder  18  through an intake port. An intake valve  22  selectively opens and closes to enable the air/fuel mixture to enter the cylinder  18 . The intake valve position is regulated by an intake camshaft  24 . A piston (not shown) compresses the air/fuel mixture within the cylinder  18 . A spark plug  26  initiates combustion of the air/fuel mixture, driving the piston in the cylinder  18 . The piston drives a crankshaft (not shown) to produce drive torque. Combustion exhaust within the cylinder  18  is forced out through an exhaust manifold  28  when an exhaust valve  30  is in an open position. The exhaust valve position is regulated by an exhaust camshaft  32 . The exhaust is treated in an exhaust system. Although single intake and exhaust valves  22 , 30  are illustrated, it can be appreciated that the engine  12  can include multiple intake and exhaust valves  22 , 30  per cylinder  18 . 
     The engine system  10  can include an intake cam phaser  34  and/or an exhaust cam phaser  36  that respectively regulate the rotational timing of the intake and exhaust camshafts  24 , 32 . More specifically, the timing or phase angle of the respective intake and exhaust camshafts  24 , 32  can be retarded or advanced with respect to each other or with respect to a location of the piston within the cylinder  18  or crankshaft position. In this manner, the position of the intake and exhaust valves  22 , 30  can be regulated with respect to each other or with respect to a location of the piston within the cylinder  18 . By regulating the position of the intake valve  22  and the exhaust valve  30 , the quantity of air/fuel mixture ingested into the cylinder  18  and therefore the engine torque is regulated. A control module  40  controls the phase angle of the intake cam phaser  34  and exhaust cam phaser  36  based on a desired torque. 
     Referring now to  FIG. 2 , a side view of the engine system  10  is shown. The exhaust camshaft  32  ( FIG. 1 ) and the intake camshaft  24  ( FIG. 1 ) are coupled to the crankshaft (not shown) via sprockets  52 A,  52 B, and  52 C and a timing chain  54 . The engine system  10  outputs a crankshaft signal  59  to the control module  40  indicating the position of the crankshaft. The crankshaft signal  59  is generated by the rotation of a wheel  56  coupled to the crankshaft. The wheel  56  can have a plurality of teeth. A wheel sensor  58  senses the teeth of the wheel and generates the crankshaft signal  59  in a periodic form. The control module  40  decodes the crankshaft signal  59  to a specific tooth number of the wheel  56 . Crankshaft position is determined from the decoded tooth number of the wheel  56 . 
     Similarly, a wheel sensor  60  senses the teeth of a wheel  62  coupled to the exhaust camshaft  32  ( FIG. 1 ) and generates a camshaft signal  63 . Camshaft position is determined from the camshaft signal  63 . As can be appreciated, a wheel (not shown) and wheel sensor (not shown) can be coupled to the intake camshaft  24  ( FIG. 1 ) either additionally or alternatively. From the camshaft position and the crankshaft position, the control module  40  can determine an overall engine position. In addition, the control module  40  can detect reverse rotation of the engine by evaluating the crankshaft signal  59  and the camshaft signal  63 . 
     Referring now to  FIG. 3 , the flow of control executed by the control module  40  according to the present invention will be described in more detail. In order to detect reverse rotation of an engine, control first determines an engine position that indicates whether the camshaft and crankshaft are synchronized. For purposes of clarity, the following discussion relates to the exhaust camshaft. As can be appreciated, a similar approach can also be applied to the intake camshaft. 
     In step  100 , the wheel sensors sense the position of the camshaft and the crankshaft. The position of the camshaft is determined relative to the position of the crankshaft. The camshaft and the crankshaft are synchronized if their states match a pre-selected pattern, and the engine has sustained it&#39;s own forward rotation as measured by crankshaft speed. If the camshaft and crankshaft are synchronized in step  110 , a state of the camshaft signal is evaluated in step  120  for a selectable region defined by a first and a second angle of the camshaft. The state of the signal can be either high or low. In step  120 , if an actual cam signal state matches a cam signal state previously sensed at the selectable region, the engine is rotating in a forward direction at step  130 . Otherwise if an actual cam signal state does not match a cam signal state previously sensed at the selectable region, the engine is rotating in a reverse direction at step  140 . 
     Referring back to step  110 , otherwise, if the camshaft and crankshaft are not synchronized, in steps  150  and  160  an edge of the camshaft sensor signal is evaluated at a region defined by a first and a second angle of the crankshaft referenced relative to top dead center of a cylinder. The reference cylinder can be selectable. The signal edge can be either low to high or high to low. In step  150 , if an actual camshaft signal edge matches an expected reverse camshaft signal edge for that region, the engine is rotating in a reverse direction at step  140 . Otherwise, in step  160 , if an actual camshaft signal edge matches an expected forward camshaft signal edge for that region, the engine is rotating in a forward direction at step  130 . Otherwise, the rotation of the engine is indeterminate at step  170 . The expected forward camshaft signal edge and the expected reversed camshaft signal edge can be selectable according to an angle of the camshaft. 
     Referring now to  FIG. 4 , an example of the reverse rotation detection method is shown for a 58× crankshaft sensor signal and a 4× camshaft sensor signal. A pulse train generated by the wheel sensor for a wheel having fifty-eight teeth that is coupled to the crankshaft is shown at  200 . Decoded teeth numbers for an engine rotating in forward direction are shown at  210 . Decoded teeth numbers for an engine rotating in reverse direction are shown at  220 . The pulse train for the crankshaft may either be generated using an edge detecting technology as shown in  230  or with a center of tooth sensing technology as shown in  240 . A pulse train generated by the wheel sensor for a wheel having four teeth that is coupled to camshaft when the cam phaser is fully advanced is shown at  260 . A pulse train generated by the wheel sensor for a wheel having four teeth that is coupled to the camshaft when the cam phaser is retarded by sixty-six crank degrees is shown at  270 . Lines A–C represent crank angles in degrees for when the piston of cylinders A–C are located at top dead center (TDC). 
     According to the present invention, an engine position is determined from a crankshaft signal and a camshaft signal. When the crankshaft and camshaft are synchronized, the cam sensor signal can be evaluated twice per one revolution of the crankshaft to determine the rotation of the engine. For example, regions shown at  280  and  282  define when the cam sensor signal can be evaluated for a 58× crank 4× cam sensing strategy. Regions  280  and  282  correspond to cam angle regions where the decoded forward teeth numbers of the crankshaft wheel are  18 – 20  and  46 – 51  respectively. The same regions are also defined by decoded reverse teeth numbers  39 – 41  and  8 – 12  respectively. The camshaft sensor signal state is compared to the previous camshaft sensor signal state for these regions  280  and  282  to determine if the engine is rotating in reverse. If the cam sensor signal state does not match the previous cam sensor signal state, the engine is rotating in reverse. 
     If the crankshaft and camshaft are not synchronized, the edges of the cam sensor signal can be evaluated at a selectable region defined by a crank angle in degrees relative to TDC for a cylinder. In the current example, the selectable region can be between 138 degrees and 150 degrees shown at  283 . Within this region, the edges of the cam sensor signal are compared against an edge of an expected cam sensor signal. The expected edge can be selectable based on an angle of the crankshaft relative to top dead center of a cylinder. If the edge matches an expected edge for reverse rotation, the engine is rotating in reverse. 
     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.