Abstract:
A method and system to start an internal combustion engine from rest is disclosed. The engine has intake and exhaust valves in each cylinder in which actuation of such valves is independent of engine rotation. The engine also has a fuel injector and a spark plug disposed in each engine cylinder. The intake and exhaust valves are closed in one engine cylinder; fuel is sprayed into such cylinder; the spark plug is fired in such cylinder. Additionally, a second cylinder is identified in which the intake and exhaust valves are closed, fuel is sprayed, and a spark is fired prior to engine rotation.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates to an internal combustion engine, which can be ignited from rest. In particular, the internal combustion engine has intake valves, which are actuated independent of engine rotation. Preferably, the engine is one in which the exhaust valves are also actuated independent of engine rotation and one in which fuel injectors are coupled directly to engine cylinders.  
       BACKGROUND OF THE INVENTION  
       [0002]     In U.S. Pat. No. 6,098,585, assigned to the assignee of the present invention, an internal combustion engine, which can be started from rest without benefit of a starter motor, is disclosed. Conventional engines are equipped with camshaft-actuated intake and exhaust valves. The camshaft or camshafts are gear or belt-driven from the engine&#39;s crankshaft. Thus, the camshaft position, and consequently the valve open/close status, is coupled to the crankshaft position. An engine at rest, therefore, has some cylinders with one valve open, some cylinders with both valves closed, and possibly one or more cylinders with both valves open. According to &#39;585, a cylinder, or cylinders, with both valves closed and with the piston in the appropriate position, can be supplied fuel and ignited to initiate engine rotation.  
         [0003]     The inventors of the present invention have recognized that an engine with intake and/or exhaust valves coupled to engine rotation, as described in &#39;585, may have at best one cylinder in a favorable position for providing the fuel in the spark. The inventors have further recognized that engine in which the actuation of the valves is decoupled from the rotation of the engine allows control over valve position so that more cylinders can be fueled and ignited to initiate engine rotation more robustly.  
       SUMMARY OF THE INVENTION  
       [0004]     A method to start an internal combustion engine from rest is disclosed. The engine has an intake valve in each cylinder in which its actuation is independent of engine rotation. The engine also has a fuel injector and a spark plug disposed in each engine cylinder. The method includes closing the intake valve in one engine cylinder, spraying fuel into the cylinder, and sparking into the cylinder, the sparking being provided by a spark plug disposed in the one engine cylinder. The method includes closing an exhaust valve, which is actuatable independent of engine rotation, prior to said sparking. The method further includes identifying a second cylinder in which the intake and exhaust valves are closed, fuel is sprayed, and a spark is fired. The valve closing, fuel spraying, and sparking occur prior to the engine rotating.  
         [0005]     An internal combustion engine having a plurality of cylinders, each of which have at least one intake valve, at least one exhaust valve, and a spark plug disposed within. The intake valve is actuatable independent of engine rotation. The cylinder also has an injector. In one embodiment, the injector is placed in the combustion chamber. In an alternative embodiment, the injector is placed in the intake port outside the The spark plug in the second cylinder is fired after the closing of the intake valve.  
         [0006]     A method to operate an internal combustion engine having at least eight cylinders is disclosed. The engine intake and exhaust valves disposed in each engine cylinder are actuatable independent of engine rotation. The engine also has a fuel injector and a spark plug disposed in each engine cylinder, the engine further having a typical order for firing of the cylinders The engine is started from rest by combusting in four engine cylinders substantially simultaneously. Pistons in a first and second of the four engine cylinders are closer to bottom dead center than positions of pistons in third and fourth cylinders; and the third cylinder underwent an intake stroke later than the fourth cylinder. Combustion is caused to occur in a next cylinder, the next cylinder being an engine cylinder next scheduled to fire after the third according to the typical order for firing of the cylinders. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     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:  
         [0008]      FIG. 1  is a schematic of an engine equipped with electromechanically-actuated poppet valves;  
         [0009]      FIG. 2  is a crank angle position diagram for a V-8 engine showing favorable positions for starting in the 8 cylinders; combustion chamber. The engine also has an electronic control unit electronically coupled to the intake valves, the fuel injectors, and the spark plugs. The electronic unit provides the following signals to a first cylinder: causing an intake valve to close, causing a fuel injector to open, and causing a spark plug to fire, the spark plug firing following the intake valve closing and the fuel injector opening wherein the engine is at rest when the signals are provided to the intake valve, the fuel injector, and the spark plug.  
         [0010]     A method to operate an internal combustion engine having an intake valve, an exhaust valve, a fuel injector, and a spark plug disposed in engine cylinders is disclosed. The actuation of the intake and exhaust valves is independent of engine rotation. The engine has a typical order for firing of the cylinders during normal operation. The method includes starting the engine from rest by combusting in at least two engine cylinders substantially simultaneously. Upon an immediately prior engine shutdown, a first of the two engine cylinders underwent an intake stroke later than a second of the two engine cylinders. Further, combustion is caused to occur in a next cylinder, which next cylinder is an engine cylinder next scheduled to fire after the first of two engine cylinders according to the typical order for firing of the cylinders.  
         [0011]     The method further includes subsequently opening and closing the exhaust valve in the second cylinder during the upward travel of the piston in the second cylinder and opening and closing the intake valve during a first half of a next piston downward movement in the second cylinder with the closing occurring after opening. Fuel is supplied to the second cylinder during the next piston downward movement in the second cylinder.  
         [0012]      FIG. 3  is a crank angle position diagram for an I-4 engine showing favorable positions for starting in the 4 cylinders; and  
         [0013]      FIG. 4  is a crank angle position for a 6-cylinder engine showing favorable positions for starting in the 6 cylinders. 
     
    
     DETAILED DESCRIPTION  
       [0014]     In  FIG. 1 , a single cylinder  13  of an internal combustion engine  10  with an electromechanical intake valve  20  and exhaust valve  19  is shown. Engine  10  contains a piston  14 , which reciprocates within cylinder  13 . Intake valve  20 , disposed in cylinder head  22 , is opened to allow gases to communicate between the combustion chamber (the volume enclosed by cylinder  13 , piston  14 , and cylinder head  22 ) and intake port  70 . When exhaust valve  19  is opened, gases are released from the combustion chamber into exhaust port  72 . In the embodiment shown in  FIG. 1 , fuel is injected into the combustion chamber by injector  16 , a configuration commonly called direct fuel injection. However, the present invention may also apply to port fuel injection, in which the fuel injector sprays fuel into intake port  70 . Intake valve  20  and exhaust valve  19  are actuated electromechanically by valve actuators  18  and  17 , respectively. Alternatively, valve actuators  17  and  18  are electrohydraulic, piezoelectric, or any other type of actuator, which allows operation of the valves independent of engine  10  rotation. In a preferred embodiment, engine  10  is a spark-ignited engine, spark plug  12  initiates combustion in the combustion chamber. The present invention also applies to engines with other types of igniters.  
         [0015]     Valve actuators  17  and  18  as shown in  FIG. 1  are electromechanical actuators. In an alternate embodiment, intake valve  19  is actuated by an electromechanical valve actuator  17  and exhaust valve  20  is actuated by a conventional camshaft. Such an arrangement is less preferred for practicing the present invention due to the lack of flexibility in actuating exhaust valve  20 , which will be discussed below.  
         [0016]     Continuing to refer to  FIG. 1 , electronic control unit (ECU)  60  is provided to control engine  10 . ECU  60  has a microprocessor  46 , called a central processing unit (CPU), in communication with memory management unit (MMU)  48 . MMU  48  controls the movement of data among the various computer readable storage media and communicates data to and from CPU  46 . The computer readable storage media preferably include volatile and nonvolatile storage in read-only memory (ROM)  50 , random-access memory (RAM)  54 , and keep-alive memory (KAM)  52 , for example. KAM  52  may be used to store various operating variables while CPU  46  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  46  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  46  communicates with various sensors and actuators via an input/output (I/O) interface  44 . Examples of items that are actuated under control by CPU  46 , through I/O interface  44 , are fuel injection timing, fuel injection rate, fuel injection duration, throttle valve position, spark plug  12  timing, actuation of valve actuators  18  and  17  to control opening and closing of intake valve  20  and exhaust valve  19 , respectively, and others. Sensors  42  communicating input through I/O interface  44  may be indicating piston position, engine rotational speed, vehicle speed, coolant temperature, intake manifold pressure, pedal position, throttle valve position, air temperature, exhaust temperature, exhaust stoichiometry, exhaust component concentration, and air flow. Some ECU  60  architectures do not contain MMU  48 . If no MMU  48  is employed, CPU  46  manages data and connects directly to ROM  50 , RAM  54 , and KAM  52 . Of course, the present invention could utilize more than one CPU  46  to provide engine control and ECU  60  may contain multiple ROM  50 , RAM  54 , and KAM  52  coupled to MMU  48  or CPU  46  depending upon the particular application.  
         [0017]     Referring to  FIG. 2 , crank angle position diagram of an 8-cylinder engine is shown. In a 4-stroke engine, any given cylinder undergoes the processes of intake, compression, expansion, and exhaust within 720 degrees, or 2 revolutions of the engine. Within that 720 degrees, one of the cylinders&#39; spark plug fires every 90 degrees of rotation. In  FIG. 2 , the 8 cylinders are shown as cylinders A, B, C, D, E, F, G, and H. The cylinders are purposely not give numerical indexes, because  FIG. 2  shows the cylinder firings happening in order. In practice, the cylinders do not fire in numerical order, but in an order to provide the least amount of unbalance, and which is consistent with the crankshaft design. Following cylinder A, during the first 180 degrees, the piston in the cylinder is in an expansion stroke, i.e., piston moving from a top dead center position toward a bottom dead center position. The piston moves upward during 180-360°. The piston in cylinder A moves downward during 360-540°; and, upward during 540-720°. The arrows in the 0-180° and 360-540° portions, for cylinder A, indicate favorable positions for igniting fuel and air in the cylinder, with the engine at rest. If the piston were in the 180-360° or 540-720° range and ignition occurred, combustion pressure would push the piston downward, causing the engine to rotate in the opposite direction of its normal direction. As many components, including the driveline and oil pumps are expecting engine rotation only in one direction, it is undesirable to allow rotation in a direction opposite to the standard direction. The arrows do not encompass the entire 0-180° interval. If the piston is too close to top dead center, there is a minimum of air above the piston. The ensuing combustion may not sufficiently push the piston down to rotate the engine far enough for starting. Thus, the piston should be at a position after top dead center by an amount, which can be determined experimentally. Also, the piston should not be at a position too close to bottom dead center. The combustion pressure acts on the piston to move it downward. When the piston reaches bottom dead center, it begins to travel upward and the combustion pressure would act to push against the piston in the wrong direction.  
         [0018]     Continuing to refer to  FIG. 2 , cylinder B is the next piston to fire after cylinder A. Thus, the processes described above in regards to cylinder A are displaced by 90°. Thus, at 180°, when the piston in cylinder A is at bottom dead center, the cylinder B is right in a favorable position for self-starting. The events in cylinder C are displaced 180° from cylinder A; cylinder D is displaced 270° and so forth.  
         [0019]     Continuing with  FIG. 2 , the two favorable positions for starting in cylinder A occur in the 0-180° and in the 360-540° windows, which are the normal downward piston strokes. If engine  10  has both intake valves  20  and exhaust valves  19 , in which their operation is fully decoupled from engine rotation, the two starting positions are equally advantageous. If, however, engine  10  has electromechanically actuated intake valves  20  and conventional camshaft-actuated exhaust valves  19 , only one of the two favorable positions for starting can be used. In the 0-180° range, cylinder A is undergoing an expansion stroke. Intake valve  20  is capable of being placed in a closed position by action of actuator  17  and exhaust valve  19  is in a closed position because cylinder A is in an expansion stroke. As discussed above, 180-360° and 540-720° ranges are unfavorable because they would cause the engine to rotate in the wrong direction. During 360-540°, cylinder A is undergoing an intake stroke. Because intake valve  20  has completely flexible events, the intake valves are capable of being closed. Exhaust valve  19  is in a closed position. However, exhaust valve  19 , which is camshaft-actuated, remains closed until the next exhaust stroke, which is about 360° later. Thus, if combustion were to occur in cylinder A in the 360-540° interval, the force of combustion pressure acts on the piston in cylinder A downwardly, causing the engine to rotate. But, during the succeeding 540-720° interval, the combustion pressure acts to stop engine  10  from rotating; the expansion work of cylinder E will not be large enough to overcome the compression work required to maintain rotation. Thus, in an engine with camshaft-actuated exhaust valves, only the bold arrows of  FIG. 2  are favorable positions in the various cylinders for starting engine  10 . All of the arrows of  FIG. 2  indicate favorable positions in the various cylinders for starting engine  10  for engine in which both intake valves  20  and exhaust valves  19  are actuated independent of engine rotation (fully variable valvetrain).  
         [0020]     The length of the arrows in  FIG. 2  are intended for illustrative purposes only and are not intended to be limiting to the present invention.  
         [0021]     Consider two cases where the engine is at rest at position X or Y. An arbitrary position X is shown in  FIG. 2 . The line at position X intersects  4  arrows, in cylinders A, D, E, and H. Thus, in an engine with a fully variable valvetrain, all of cylinders A, D, E, and H can be caused to control intake and exhaust valves, provided with fuel, and provided with ignition. The ensuing combustion in these 4 cylinders causes the engine to rotate, thereby compressing air in other cylinders and allowing engine combustion to occur in those other cylinders. If the arbitrary Y is considered, only two cylinders, A and E, have favorable positions intersecting with Y. In this situation, there are two cylinders to be used for starting engine  10 . Inspection of all positions in  FIG. 2  indicates that there are 2 favorable cylinders available for ignition at the least and 4 at the most. If engine  10  has camshaft-actuated exhaust valves  19 , the number of cylinders available for self-starting is either 1 or 2, depending on the arbitrary position at which engine  10  stopped.  
         [0022]     A crank angle position diagram for a 4-cylinder engine is shown in  FIG. 3 . In the 720°, during which all 4 cylinders have a combustion event, a cylinder fires every 180°. At arbitrary positions X and Y, cylinders A and C are both in a favorable position for ignition. At arbitrary position Z, no cylinders are in a favorable position for ignition. Thus, if engine  10  were to stop in a position corresponding to position Z in the cycle, it would be impossible to start engine  10  from such position. However, there are measures that can be taken to ensure that the engine stops in a favorable position for restarting, such as shown in published application U.S. 2004-0123831, assigned to the assignee of the present invention.  
         [0023]     A crank angle position diagram for a 6-cylinder engine, is shown in  FIG. 4 , in which a cylinder fires every 120°. At position X, cylinders A, C, D, and F are in favorable positions for starting. However, the existence of 4 cylinders to start the engine depends on the length of the arrows, i.e., the exact period for favorable starting. As discussed above, the exact period can be determined experimentally and depends on variables such as engine friction in the engine, engine architecture, etc. At position Y, cylinders A and D are in a favorable position. Depending on the length of the favorable positions for starting, it is possible that there would be a position, such as position Z in  FIG. 3 , in which no cylinders are in a favorable position. As discussed above, measures could be taken to ensure that the engine does not stop in such a position. Also, as discussed above, if the engine has camshaft-actuated exhaust valves, half as many cylinders would be available, at any given position, for favorable starting than with an engine with a fully variable valvetrain.  
         [0024]     Six-cylinder engines are built in inline-6, 60° vees, and 90° vees commonly. All of these engines have firing of the cylinders occurring every 120°; thus,  FIG. 4  applies to all these configurations. The cylinder designations A-F do not indicate the cylinder firing order, which order depends on the engine configuration.  
         [0025]     As shown in  FIG. 1 , fuel injector  16  is mounted in the combustion chamber. Alternatively, fuel injector  16  is mounted in intake port  70 . In this case, fuel is injected prior to intake valve  20  being caused to close. A portion of the fuel injected by injector  16  diffuses into the combustion chamber past intake valve  20 . Additionally, the fuel may drip from intake port walls into the combustion chamber. Furthermore, if there are temperature gradients, convective currents may be set up causing fuel to be carried into the combustion chamber. After a period of time elapses, i.e., a period of time to ensure that a sufficient amount of fuel has been transported into the combustion chamber, intake valve  20  is closed and combustion is initiated afterward.  
         [0026]     The illustration of a single cylinder of engine  10  in  FIG. 1  shows one intake valve and one exhaust valve. It is common to have two or more intake valves and two or more exhaust valves per cylinder. For the present invention, all intake valves and all exhaust valves are closed prior to initiating combustion in the cylinder. Otherwise, an open valve would allow the combustion-generated pressure to escape through the valve.  
         [0027]     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.