Abstract:
A control method and apparatus for a variable engine valve operating control mechanisms which move the engine valves to a safe lift/timing position with respect to a piston to minimize the potential for valve to piston contact during valve surge. At least one engine operating conditions is selected and provided with a threshold triggering a control to move the valves to a safe position in a calibrated, predictive manner in advance of any potential valve to piston contact. The control method and apparatus can be integrated into the existing engine control and variable valve operating control mechanism.

Description:
BACKGROUND 
     The present description relates, in general, to internal combustion engines and, more particularly, internal combustion engines having variable valve operating characteristics. 
     Internal combustion engines use a timed coordination between intake and exhaust valves and a reciprocating piston within each cylinder to control the flow of intake charge into the cylinder and the flow of combustion exhaust gases from the cylinder. 
     In the past, the amount of movement of the intake and exhaust valves with respect to the intake and exhaust combustion chamber ports was fixed. Recent engine developments have allowed for variable valve characteristics in response to varying engine load, speed and other operating conditions. 
     Generally, the variable valve operating mechanism changes the lift, timing or operating angle of the valve. For example, such a mechanism can allow valve actuation from a low lift state at low engine speed or loads to a higher lift for greater valve stroke distance into the engine cylinder and a greater port opening at higher operating speeds and/or loads to allow for increased intake charge flow into the cylinder and to achieve increased engine efficiency. 
     However, in a high valve lift mode of operation, the clearance between the valve and the piston decreases. During an engine over-rev, which can be caused by miss-shifting, this causes valve surge in which the valves cannot strictly follow the cam profile, particularly during valve closing. Generally speaking, valve surge or float occurs when the valve springs does not have sufficient force to follow a valve closing cam profile. The resulting contact between the valve and the piston can cause catastrophic engine failure. 
     It would be desirable to provide a variable valve operating control method and apparatus which minimizes the possibility of valve to piston contact. 
     SUMMARY 
     An internal combustion engine valve operation control apparatus for at least one of an intake valve and an exhaust valve movably disposed with respect to an engine cylinder to open and close a port in the engine combustion chamber in a timed relationship to the position of a piston reciprocally mounted in the engine cylinder, includes an intake and an exhaust valve movement actuator coupled to the at least one of the intake valve and the exhaust valve to control movement of the at least one of the intake valve and the exhaust valve between engine combustion chamber port closed and port open positions in response to changes in engine operating parameters. A control receives engine operating parameter signals from the engine, and controls the valve movement actuator to move the at least one of the intake valve and the exhaust valve to a safe position with respect to the piston in the engine cylinder under predetermined engine operating conditions to prevent contact between the at least one of the intake valve and the exhaust valve and the piston. 
     The intake and exhaust valve movement actuator variably positions the at least one of the intake valve and the exhaust valve in one of a low lift position where the at least one of the intake valve and the exhaust valve extends a small distance into the cylinder at a valve open position at a first engine operation state and a high lift position where the at least one of the intake valve and the exhaust valve extends a greater distance into the cylinder during a second engine operating condition. 
     The control moves the intake and exhaust valve movement actuator to move the at least one of the intake valve and the exhaust valve to the safe position as the engine operating conditions move from the first state toward the second state. 
     The control is responsive to the rate of change of engine operating conditions moving from the first state toward the second state. 
     The control executes a stored program of engine operating conditions setting a threshold of one engine operating condition associated with contact of the at least one intake exhaust valve with the piston. 
     In one aspect, the engine operating condition is engine speed, and the threshold is a predetermined engine speed. 
     In another aspect, the engine operating condition is engine speed, and the threshold is a predetermined rate of increase in engine speed. 
     The calibratible engine speed is determined, for predetermined rate of increase in engine speed, that corresponds to a likelihood of contact between the at least one of the intake valve and the exhaust valve with the piston. The control, in response to the engine speed reaching the predetermined speed, controls the intake and exhaust valve movement actuator to move the at least one of the intake valve and the exhaust valve to the safe position. 
     In one aspect, the engine operating condition is a predetermined acceleration rate of the engine above an expected acceleration rate of engine operation. 
     In one aspect, the control moves the at least one of the intake valve and the exhaust valve to a safe position defined by movement of the valve from a high lift state toward a low lift state. In another aspect, the control, in response to engine operating conditions, moving the at least one of the intake valve and the exhaust valve to the safe position by varying the value timing or by reducing the preset valve open time duration. 
     A method of controlling the position of at least one of an intake valve and an exhaust valve in one combustion chamber of an internal combustion engine with respect to piston position in the combustion chamber based on engine operating conditions includes: 
     sensing at least one engine operating conditions; 
     comparing the current value of the at least one engine operating condition with prestored values of the at least one intake and exhaust valve position with respect to the position of the piston in the combustion chamber; 
     establishing a threshold value of the engine operating condition and the preset valve position above which an increase in the engine operating condition increases the possibility of contact between the at least one of the intake valve and exhaust valve with the piston; and when the threshold value is met, moving the at least one of the intake valve and the exhaust valve to a safe position to minimize potential contact with the piston. 
     The method also includes the step of establishing the threshold and the predetermined rate of change of engine operating conditions with respect to the one of the intake valve and the exhaust valve engine cycle positions. 
     In one aspect, the method sets the predetermined engine operating condition as engine speed. 
     Where the at least one of the intake valve and the exhaust valve moves between a low lift and a high lift position depending upon the engine operating condition, the method moves at least one of the intake valve and the exhaust valve from the high lift position toward the low lift position when the threshold is met. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The various features, advantages and other uses of the present variable valve operating control method and apparatus will become more apparent by referring to the following detailed description and drawing in which: 
         FIG. 1  is a perspective view of the variable valve operating apparatus showing the intake valves for a single engine cylinder of a multi-cylinder engine; 
         FIG. 2  is a schematic diagram of the variable valve operating control apparatus partially shown in  FIG. 1 ; 
         FIG. 3  is a block diagram of the variable valve operating control apparatus shown in  FIGS. 1 and 2 ; 
         FIGS. 4A and 4B  are pictorial representations of the variable valve control apparatus shown in  FIG. 1  depicting the intake valve in closed and low lift open positions; 
         FIGS. 5A and 5B  are pictorial representations of the variable valve control apparatus shown in  FIG. 1  depicting the intake valve in closed and high lift open positions; 
         FIG. 6A  is a graph depicting engine speed versus time where the engine speed increase rate is within an expected range of operation to show one aspect of a valve operating control method and apparatus; 
         FIG. 6B  is a graph depicting engine speed and time where the engine speed increase rate exceeds expected range of operations and depicting another aspect of a valve operation control method and apparatus; 
         FIG. 7A  is a flow chart depicting the sequence control steps for implementing the aspect of the valve operating control method and apparatus depicted in  FIG. 6A ; and 
         FIG. 7B  is a flow chart depicting the sequence control steps for implementing the aspect of the valve operating control method and apparatus depicted in  FIG. 6B . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawing, into  FIGS. 1-7B  in particular, there is depicted a variable valve operating control apparatus and method which minimizes the possibility of contact between an intake and/or an exhaust valve and a piston under certain engine operating conditions. 
     In the following description, the following terms have the meaning set forth herein and/or are calculated or measured as described below. 
     Engine Speed-calculated from crankshaft position sensor value. 
     Valve Angle-calculated from camshaft position sensor signal. 
     Engine Load-calculated from intake air amount measured by an airflow sensor. 
     Valve Operating Angle-the total crank angle of which a valve is opened (proportional to valve lift in some variable valve control mechanisms). 
     Valve Lift-the distance (in millimeters) that a valve moves between closed and fully opened positions. 
     Valve Timing-when a valve opens and/or closes, measured in degrees of crankshaft angular position (also referred to as crank angle). 
     Variable Valve Timing (VVT)-the control that varies valve timing with different engine operating conditions. 
     The present variable valve operating control method and apparatus may be used with any internal combustion engine which has variable valve operating characteristics controls which are capable of varying the valve operating characteristics under varying engine speed, load and operating conditions. The present variable valve operating control method and apparatus is usable with any internal combustion engine, regardless of the number of combustion chambers, the number of intake valves per combustion chamber, or the number of exhaust valves per combustion chamber. 
     It will be understood that, although the following description and drawings illustrate the present variable valve control method and apparatus in conjunction with a pair of intake valves associated with one engine combustion chamber, the method and apparatus are employable with the single intake valve or a single exhaust valve on a single engine combustion chamber, only on the intake valve or valves of each engine combustion chamber, only on the exhaust valve or valves of each engine combustion chamber, or on both of the intake and exhaust valve or valves on each combustion chamber of an engine. 
       FIG. 1  depicts one example of a variable valve operating control method and apparatus  20  which is capable of varying any one or more of an intake or exhaust valve operating characteristics during engine operation. 
     By way of example,  FIG. 1  depicts a pair of intake valves  22  and  24  associated with one engine combustion chamber. 
     As explained in greater detail in U.S. Pat. No. 7,299,775, the contents of which are incorporated herein in its entirety, the variable valve control includes an intake and/or exhaust valve movement actuator in the form of a control shaft  26  driven by a motor  28  under the control of an actuator  30 . The actuator  30 , as described hereafter, is responsive to signals from the engine control unit (ECU)  31  which is in turn responsive to various engine operating parameters, such as engine speed, load, etc. It will be understood that the following description of the variable valve operating mechanism is by way of example only as any type of mechanism for varying an operating parameter of an intake and/or an exhaust valve of an internal combustion engine can employ the present control method and apparatus. 
     As explained in the above-identified patent, the actuator  30  is coupled to the motor  28  which controls the linear reciprocal movement of the control shaft  26 . This changes the angles of interaction of the control shaft  26  with a roller arm  32 , roller rocker  34  for each intake valve  22  or  24 , and the cam shaft  36  (in  FIGS. 4A and 4B ) to thereby change the amount of lift or movement for opening or closing the intake valves  22  and  24 . 
     As shown in  FIGS. 4A and 4B , at idle or low engine operating speeds, the control shaft  26  is positioned by the actuator  30  and the motor  28  so as to allow movement of the intake valve  22  from the fully closed position shown in  FIG. 4A  to the fully opened position shown in  FIG. 4B  with only a small amount of valve lift or opening movement as denoted by the low lift dimension  40 . Similarly, and as described hereafter, at higher engine operating speeds and/or engine loads, the variable valve operating mechanism changes the interaction of the control shaft  26 , the roller rocker  34 , the roller arm  32  and the cam shaft  36  to create a greater distance of valve lift or movement between the fully closed valve position shown in  FIG. 5A  and the fully open position of the intake valve  22  for a so-called high lift position  44 . 
     In order to prevent contact between the valve, such as one of the intake valves  22  and  24  and the top of the piston during high lift modes of operation of the intake valves  22  and  24 , the present method and apparatus create a look-up table containing data stored in a memory accessed by the ECU  31  which represents one or more engine operating parameters to detect the approach of one or more engine operating parameters to detect the potential contact between an intake valve  22  and  24  and the piston. 
     One aspect of the operation of the apparatus performing the control method is shown in  FIGS. 6A and 7A .  FIG. 6A  represents a graph of engine speed and RPMs over time where the engine speed is gradually increasing within an expected range of acceleration along line  60 . An engine speed  62  is calculated at which valve surge is possible depending upon the design tolerances of a particular engine. This speed  62  is shown on the engine speed line  60  in the graph of  FIG. 6A . 
     Generally, the present method and apparatus anticipate an engine speed where a valve surge is possible. At a predetermined engine speed prior to the engine speed  62 , such as engine speed  64  on graph line  60 , the ECU  31 , taking into account the time required to return the valve position to a safe position, described hereafter, will send signals to the actuator  30  to move the control shaft  26  in a direction to return the valve, such as intake valves  22  and  24  associated with one combustion chamber of the engine, to a safe position. The safe position is determinable with respect to each engine and generally is a position where the amount of valve lift or the valve timing is such to minimize any possibility of contact between the intake valve  22  or  24  and the piston. The safe position can be, but does not necessarily have to be, the low lift or low valve open position shown in  FIG. 4B . The safe position can also be any other position between the high lift position of the valve and the fully closed position of the valve. The safe position can be any position where contact between the intake valves  22  or  24  in the piston is minimal or non-existing. 
     The safe position can also be a variation in the valve timing such as a variation in the valve operating angle for a variation in valve timing due to a change in the valve opening and valve closing crank angle. 
     The ECU  31  takes into account the time it takes to return the valves  22  and  24  to the safe position. This can be a variable amount of time depending upon the amount of valve timing. Thus, the ECU  31  at engine speed  64  on graph line  60  will send signals to the actuator  30  to move the control shaft  26  in a direction to begin to return the intake valves  22  and  24  to the predetermined safe position. This can cause a variation of the valve timing so that the amount of valves open or time duration is immediately reduced, or the valve lift is varied to cause retraction of the valve towards the closed position. 
     As shown in  FIG. 7A , the ECU  31  executes a control program which determines in step  70  that engine preconditions are met, with respect to engine operating parameters including oil temperature, lack of relevant diagnostic malfunctions present, etc. The engine speed and engine load are then detected in step  72 . The ECU  31 , in step  74 , then determines the engine valve position or state, such as valve lift, valve timing or valve opening duration. Depending on the valve intake positions, the engine speed and the engine load, the ECU  31  in step  76  may command the intake valves  22  and  24  via adjustments in the linear position of the control shaft  26  to move to safe states or positions with respect to the piston to prevent less risk of damage due to valve to piston contact during valve surge after the engine speed reaches a predetermined or certain threshold level, such as denoted by engine speed  64  in  FIG. 6A . 
     The graph line  60  in  FIG. 6A  depicts the calculated acceleration rate for an expected acceleration increase within normal range of operation of the engine. With appropriate tolerances, the graph line  60  can be stored in memory as a look-up table accessible by the ECU  31  when the engine is operating. If the engine speed increase rate or acceleration of the engine follows the graph line  60  or is below the graph line  60 , the ECU  31  when the engine speed  64  on the graph line  60  is reached, will implement protective action to move the intake valves  22  and  24  to the safe position. 
     The movement of the safe position can constitute simply moving the intake valves  22  and  24  toward, but not fully to the closed position. Alternately, the ECU  31  can implement action to move the intake valves  22  and  24  to the safe position defined by altering, or decreasing the valve open duration time. This has the effect of moving the intake valves  22  and  24  toward the low lift or closed position prior to the programmed normal end of the valve open time duration. 
       FIG. 6B  depicts a similar engine speed versus time graph. In  FIG. 6B , a separate graph line  90  is shown to represent an engine speed increase rate or acceleration exceeding an expected engine range of operation. The data represented by this graph line is calibrated for each particular engine type, but generally indicates an over-speed or over-rev condition. Prior to reaching an engine speed at which valve surge is likely to occur, as denoted by engine speed  92 , the ECU  31 , as shown in  FIG. 7B , executes a stored program utilizing the valve surge look-up table stored in memory to initiate repositioning of the valve to a safe state taking into account the time to return the valve position, either lift and/or timing, to the safe position and upon the then current valve timing, lift position, valve operating angle etc. 
     Referring now to  FIG. 7B , the ECU  31  executes the same steps in conjunction with the logic detection shown in  FIG. 7B  as it did with the general speed increase shown in  FIG. 6A and 7A  by determining the engine preconditions on map in step  70 . Engine speed and engine load and then detected in step  72 . The rate of engine speed increase or acceleration is determined in step  74  and compared with calibratible values for the particular engine in step  76 . If the rate of engine speed increase is within expected front engine parameters as shown by step  78 , the ECU  31  determines the engine valve state, such as valve lift, timing, etc. in step  80  and commands the valve, further look-up table or equivalent to the particular valve position. For example, higher engine speeds are associated with higher lifts for intake and exhaust valves and latest or most retarded closing time. 
     Alternately, if the comparison in step  76  yields a determination that the determined rate of engine speed increase in steps  76  is not within an expected range of engine operations and exceeds a calibratible threshold as shown by step  82 , the ECU  31  issues commands to reposition the control shaft  26  to move the intake valves  22  and  24  to the safe state, as described above, which, in step  84 , presents less risk of damage from valve to piston contact during the valve surge. 
     The graphical values along the graph line  90  in the graph depicted in  FIG. 6B  represent engine speed increase rates or acceleration exceeding an expected range of operation of the vehicle engine. When the engine speed increase rate, is calculated by the ECU from the engine speed and other factors approaches or reaches an engine speed corresponding to the graphical point  91 , the ECU, using the separate look-up table from that employed with the normal expected range of engine acceleration shown in  FIG. 6A , will move the intake valves  22  and  24  to the safe position as described above. 
     It should be noted that the graphical point  91  on the graph in  FIG. 6B  is earlier in time than the similar point  64  on the graph line  60  in  FIG. 6A . This time difference takes into account the increased acceleration rate depicted by the graph in line  90  in  FIG. 6B  which requires an earlier start to begin movement of the intake valves  22  and  24  to a safe position since the engine is accelerating at a higher rate toward the engine speed  92  at which valve surge is likely to occur and there is less time before the engine reaches the preset speed  92 . 
     Since the time required to return the intake valves  22  and  24  to the safe position is about the same in each engine operating condition shown by the graphs in  FIGS. 6A and 6B , the ECU, using the values in the different look-up tables, must begin to move the intake valves  22  and  24  towards the safe position at an earlier point in the acceleration line since, in the engine operating condition depicted by  FIG. 6B , the engine is accelerating at a rate exceeding expected engine range of operation and therefore is likely to reach engine speed at which valve surge is likely to occur in a shorter amount of time than when the engine speed increase rate is within the expected range of operation as shown in  FIG. 6A .