Abstract:
A method of protecting an intake manifold of an engine of a hybrid propulsion system including an electric motor comprises detecting a reverse rotation of an engine. A fuel injector of the engine that is rotating in reverse is commanded to cease operation. A spark plug of the engine that is rotating in reverse is commanded to cease operation. The ceasing of reverse rotation of the engine is then confirmed.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to internal combustion engines, and more particularly to systems and methods for protecting an intake manifold during reverse engine rotation.  
       BACKGROUND OF THE INVENTION  
       [0002]     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.  
         [0003]     Conventional engines will rarely rotate in reverse for long periods 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.  
         [0004]     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.  
         [0005]     In addition to damage to the intake manifold, reverse rotation of the engine may cause further problems such as excess bearing wear and damage to gaskets, hoses and sensors connected to the intake manifold.  
       SUMMARY OF THE INVENTION  
       [0006]     A method of protecting an intake manifold of an engine of a hybrid propulsion system including an electric motor comprises detecting a reverse rotation of an engine. A fuel injector of the engine that is rotating in reverse is commanded to cease operation. A spark plug of the engine that is rotating in reverse is commanded to cease operation. The ceasing of reverse rotation of the engine is then confirmed.  
         [0007]     In another feature, the method comprises notifying a diagnostic module of the reverse rotation.  
         [0008]     In another feature, an electric motor is commanded to cease operation after detecting reverse rotation is performed, wherein commanding the electric motor to cease operation further comprises commanding the electric motor to begin forward rotation.  
         [0009]     In another feature, the method comprises commanding the fuel injector to re-enable and commanding the spark plug to re-enable after confirming of the ceasing of reverse rotation of the engine is performed.  
         [0010]     In other features, detecting reverse rotation comprises comparing an actual cam sensor signal to an expected cam sensor signal. Wherein the expected cam sensor signal is determined based on the actual cam sensor signal and a crankshaft sensor signal.  
         [0011]     In other features, the expected cam sensor signal is set to a previously stored actual cam sensor signal, and wherein detecting reverse rotation further comprises comparing a state of the actual cam sensor signal to a state of the expected cam sensor signal while the engine is operating in at least one of a first region and a second region and when a camshaft and crankshaft are synchronized.  
         [0012]     In still other features, the expected cam sensor signal is set to an expected reverse cam sensor signal, and wherein detecting reverse rotation further comprises comparing an edge of the actual cam sensor signal to an edge of the expected cam sensor signal for a selected crank angle region relative to top dead center of a specified cylinder when a camshaft and crankshaft are not synchronized.  
         [0013]     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  
       [0014]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0015]      FIG. 1  is a schematic illustration of a hybrid propulsion system including the intake manifold protection system according to the present invention;  
         [0016]      FIG. 2  is a flowchart illustrating the steps for identifying reverse rotation of an engine of the propulsion system; and  
         [0017]      FIG. 3  is a flowchart illustrating the intake manifold protection method according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     The following description of the preferred embodiment(s) 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 the same 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.  
         [0019]     Referring now to  FIG. 1 , an engine propulsion 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  is electronically controlled to regulate 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 propulsion system of the present invention can be implemented in engines having a plurality of cylinders including, but not limited to, 2, 3, 5, 6, 8, 10, 12 and 16 cylinders.  
         [0020]     A fuel injector  20  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  28  to produce drive torque.  
         [0021]     Combustion exhaust within the cylinder  18  is forced out through an exhaust manifold  30  when an exhaust valve  32  is in an open position. The exhaust valve position is regulated by an exhaust camshaft  34 . The exhaust is treated in an exhaust system (not shown). Although single intake and exhaust valves  22 , 32  are illustrated, it can be appreciated that the engine  12  can include multiple intake and exhaust valves  22 , 32  per cylinder  18 . An electric motor  36  provides an alternate source of power needed to rotate the crankshaft  28  of the engine  12 . A control module  38  senses inputs from the engine system and responds by controlling the aforementioned components of the propulsion system  10 .  
         [0022]     Control module  38  can determine when the engine  12  is operating in reverse rotation by evaluating a pulse train signal generated by a cam sensor  40  and a pulse train generated by a crankshaft sensor  41 . Referring now to  FIGS. 1 and 2 , the flow of control executed by the control module  38  according to the present invention will be described in more detail. In order to detect reverse rotation of an engine  12 , control first determines an engine position that indicates whether the camshaft  24  and crankshaft  28  are synchronized. For purposes of clarity, the following discussion relates to the intake camshaft  24  (hereinafter referred to as camshaft  24 ). As can be appreciated, a similar approach can also be applied to the exhaust camshaft  34 .  
         [0023]     In step  100 , the sensors sense the position of the camshaft  24  and the crankshaft  28 . The. position of the camshaft  24  is determined relative to the position of the crankshaft  28 . The camshaft and the crankshaft are synchronized if their states match a preselected pattern, and the engine has sustained it&#39;s own forward rotation as measured by crankshaft speed. If the camshaft  24  and crankshaft  28  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  24 . 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  12  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  12  is rotating in a reverse direction at step  140 .  
         [0024]     Referring back to step  110 , otherwise, if the camshaft  24  and crankshaft  28  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 position referenced relative to top dead center of a cylinder  18 . The reference cylinder  18  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  12  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  12  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.  
         [0025]     Referring now to  FIGS. 1 and 3 , once control determines the engine  12  is rotating in reverse, subsequent actions are taken to protect the intake manifold  14 .  FIG. 3  is a flowchart illustrating the steps taken by the control module  38 . In step  200 , control commands the electric motor  36  to stop reverse rotation. In step  210 , control disables fuel by commanding the fuel injector  20  to cease operation. In step  220 , control disables spark by commanding the spark plug  26  to cease firing. The actions of steps  210  and  220  are likely to occur at the same time. In step  230 , control will notify an on-board diagnostic module of the reverse rotation condition. The diagnostic module can set a diagnostic code and perform any diagnostic functions if the diagnostic module determines to do so. Once reverse rotation has stopped  240 , control re-enables fuel in step  250  by commanding the fuel injector  20  to inject fuel, re-enables spark in  260  by commanding the spark plug  26  to initiate combustion, and exits the loop.  
         [0026]     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.