Patent Publication Number: US-9885260-B2

Title: Methods and system for operating an exhaust valve of an internal combustion engine

Description:
FIELD 
     The present description relates to methods and a system for operating an exhaust valve of an internal combustion engine. The methods and systems may be particularly useful for engines that may operate with higher exhaust pressures. 
     BACKGROUND AND SUMMARY 
     An internal combustion engine inducts air to mix with fuel for combustion. Combusting the air and fuel raises pressure in engine cylinders which is translated into torque via engine pistons and a crankshaft. Exhaust gas exits the cylinders to make way for subsequent combustion events in the cylinder. The flow of exhaust gas from engine cylinders may be restricted by a catalyst or another device in the exhaust system such as a turbocharger turbine. At higher engine speeds and loads, pressure of exhaust gas in the exhaust manifold may be sufficiently high to cause closed exhaust valves to temporarily open. In particular, exhaust pressure acting on a back side of exhaust valves may be sufficient enough to overcome exhaust valve spring pressure, thereby opening one or more engine exhaust valves. An exhaust valve that opens in an untimely manner may reduce engine efficiency and degrade engine performance. Therefore, it may be desirable to provide a way of reducing the possibility of an exhaust valve opening when it is expected to be closed. 
     The inventors herein have recognized the above-mentioned issues and have developed a an engine operating method, comprising: locking an exhaust valve of a cylinder in a closed position via a mechanism other than a valve spring in response to the exhaust valve being in mechanical communication with a base circle of a camshaft lobe. 
     By locking an exhaust valve in a closed position while the exhaust valve is in communication with a base circle of a camshaft, it may be possible to prevent the exhaust valve from opening at times when exhaust valve opening may be undesirable. An exhaust valve is in mechanical communication with, or in direct or indirect contact with, the exhaust cam lobe base circle when the exhaust valve or a tappet in contact with the exhaust valve is contacting the exhaust cam lobe base circle, but the exhaust valve may not be in contact or mechanical communication with the exhaust cam base circle through the exhaust cam lobe itself. For example, during high engine load conditions, exhaust valves may be locked closed so that exhaust pressure from other engine cylinders may be prevented from opening closed exhaust valves so that cylinder charge may not be diluted with excess exhaust gas recirculation. The exhaust valve locking mechanism may be mechanically driven or it may be electromechanically driven. In one example, exhaust valves may be locked via inserting a pawl into a groove in a stem of an exhaust valve. The pawl holds the exhaust valve closed in the presence of higher exhaust pressures. 
     The present description may provide several advantages. Specifically, the approach may reduce the possibility of untimely exhaust valve openings. Further, the approach may be accomplished via mechanical or electromechanical mechanisms. Additionally, diagnostics may be made part of the approach so that mitigating actions may be taken if the exhaust valve locking mechanism degrades. 
     The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages described herein will be more fully understood by reading an example of an embodiment, referred to herein as the Detailed Description, when taken alone or with reference to the drawings, where: 
         FIG. 1  is a schematic diagram of an engine; 
         FIGS. 2A-2D  show several views of a first embodiment of an exhaust valve locking mechanism; 
         FIGS. 3A-3C  show several views of a second embodiment of an exhaust valve locking mechanism; 
         FIGS. 4A-4C  show several views of a third embodiment of an exhaust valve locking mechanism; 
         FIG. 5  shows plots of a sequence for operating an exhaust valve locking mechanism; 
         FIG. 6  is a flowchart of a method for operating an exhaust valve; and 
         FIG. 7  is a flowchart of a method detecting exhaust valve locking mechanism degradation. 
     
    
    
     DETAILED DESCRIPTION 
     The present description is related to operating an internal combustion engine of a vehicle. Exhaust valves may be locked in a closed position to reduce the possibility of exhaust gas entering engine cylinders at undesirable times. The internal combustion engine may be configured as is shown in  FIG. 1 . The engine of  FIG. 1  may include exhaust valves and exhaust valve locking mechanisms as is shown in  FIGS. 2A-4C . The exhaust valve locking mechanism may operate according to the sequence shown in  FIG. 5 . The exhaust valve locking mechanism may be operated by the method of  FIG. 6 . The exhaust valve locking mechanism may be diagnosed according to the method of  FIG. 7 . 
     Referring to  FIG. 1 , internal combustion engine  10 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 1 , is controlled by electronic engine controller  12 . Engine  10  is comprised of cylinder head  35  and block  33 , which include combustion chamber  30  and cylinder walls  32 . Piston  36  is positioned therein and reciprocates via a connection to crankshaft  40 . Flywheel  97  and ring gear  99  are coupled to crankshaft  40 . Starter  96  (e.g., low voltage (operated with less than 30 volts) electric machine) includes pinion shaft  98  and pinion gear  95 . Pinion shaft  98  may selectively advance pinion gear  95  to engage ring gear  99 . Starter  96  may be directly mounted to the front of the engine or the rear of the engine. In some examples, starter  96  may selectively supply torque to crankshaft  40  via a belt or chain. In one example, starter  96  is in a base state when not engaged to the engine crankshaft. Combustion chamber  30  is shown communicating with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  and exhaust valve  54 . Each intake and exhaust valve may be operated by an intake cam  51  and an exhaust cam  53 . The position of intake cam  51  may be determined by intake cam sensor  55 . The position of exhaust cam  53  may be determined by exhaust cam sensor  57 . Intake valve  52  may be selectively activated and deactivated by valve activation device  59 . Exhaust valve  54  may be selectively activated and deactivated by valve activation device  58 . Valve activation devices  58  and  59  may be electro-mechanical devices. Exhaust valve locking device  60  may lock exhaust valve  54  in a closed position. 
     Fuel injector  66  is shown positioned to inject fuel directly into cylinder  30 , which is known to those skilled in the art as direct injection. Fuel injector  66  delivers liquid fuel in proportion to the pulse width from controller  12 . Fuel is delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). In one example, a high pressure, dual stage, fuel system may be used to generate higher fuel pressures. 
     In addition, intake manifold  44  is shown communicating with turbocharger compressor  162  and engine air intake  42 . In other examples, compressor  162  may be a supercharger compressor. Shaft  161  mechanically couples turbocharger turbine  164  to turbocharger compressor  162 . Optional electronic throttle  62  adjusts a position of throttle plate  64  to control air flow from compressor  162  to intake manifold  44 . Pressure in boost chamber  45  may be referred to a throttle inlet pressure since the inlet of throttle  62  is within boost chamber  45 . The throttle outlet is in intake manifold  44 . In some examples, throttle  62  and throttle plate  64  may be positioned between intake valve  52  and intake manifold  44  such that throttle  62  is a port throttle. Compressor recirculation valve  47  may be selectively adjusted to a plurality of positions between fully open and fully closed. Waste gate  163  may be adjusted via controller  12  to allow exhaust gases to selectively bypass turbine  164  to control the speed of compressor  162 . Air filter  43  cleans air entering engine air intake  42 . 
     Distributorless ignition system  88  provides an ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  48  upstream of catalytic converter  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . 
     Converter  70  can include multiple catalyst bricks, in one example. In another example, multiple emission control devices, each with multiple bricks, can be used. Converter  70  can be a three-way type catalyst in one example. 
     Controller  12  is shown in  FIG. 1  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , read-only memory  106  (e.g., non-transitory memory), random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a position sensor  134  coupled to an accelerator pedal  130  for sensing force applied by foot  132 ; a position sensor  154  coupled to brake pedal  150  for sensing force applied by foot  152 , a measurement of engine manifold pressure (MAP) from pressure sensor  122  coupled to intake manifold  44 ; an engine position sensor from a Hall effect sensor  118  sensing crankshaft  40  position; a measurement of air mass entering the engine from sensor  120 ; and a measurement of throttle position from sensor  68 . Barometric pressure may also be sensed (sensor not shown) for processing by controller  12 . In a preferred aspect of the present description, engine position sensor  118  produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined. 
     During operation, each cylinder within engine  10  typically undergoes a four stroke cycle: the cycle includes the intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, generally, the exhaust valve  54  closes and intake valve  52  opens. Air is introduced into combustion chamber  30  via intake manifold  44 , and piston  36  moves to the bottom of the cylinder so as to increase the volume within combustion chamber  30 . The position at which piston  36  is near the bottom of the cylinder and at the end of its stroke (e.g., when combustion chamber  30  is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). 
     During the compression stroke, intake valve  52  and exhaust valve  54  are closed. Piston  36  moves toward the cylinder head so as to compress the air within combustion chamber  30 . The point at which piston  36  is at the end of its stroke and closest to the cylinder head (e.g., when combustion chamber  30  is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In a process hereinafter referred to as ignition, the injected fuel is ignited by known ignition means such as spark plug  92 , resulting in combustion. 
     During the expansion stroke, the expanding gases push piston  36  back to BDC. Crankshaft  40  converts piston movement into a rotational torque of the rotary shaft. Finally, during the exhaust stroke, the exhaust valve  54  opens to release the combusted air-fuel mixture to exhaust manifold  48  and the piston returns to TDC. Note that the above is shown merely as an example, and that intake and exhaust valve opening and/or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples. 
       FIG. 2A  shows a first example of an exhaust valve locking device  60 . The exhaust valve locking device  60  is shown in a base position where exhaust valve  54  is locked to prevent exhaust valve  54  from opening. 
     Exhaust valve  54  is shown with groove  220  cut crosswise into exhaust valve shaft  201 . A cylindrical land  221  connects upper shaft  201   b  and lower shaft  201   a . Exhaust valve locking device includes a pawl  204  which is inserted into groove  220  when exhaust valve locking device  60  is in its base position. Pawl  204  may slide back and forth in a channel (not shown) of cylinder head  35  which provides support to pawl  204  and exhaust valve  54  when pawl  204  is engaged in groove  220 . Pawl  204  is mechanically coupled to a first protrusion  208  via linkage  206 . First protrusion  208  is mechanically coupled to shaft  214 . Spring  212  biases shaft  214  in the base position as shown. Shaft  214  is mechanically coupled to first protrusion  208  and second protrusion  210 . Pawl  204  may move in the directions shown by arrow  202  such that pawl  204  moves in and out of groove  220 . In the base position, exhaust camshaft  53  is not in mechanical communication with exhaust valve locking device  60 . 
     Exhaust camshaft  53  includes camshaft lobe  250 , which may selectively provide lift to open exhaust valve  54  when camshaft  53  rotates. Exhaust camshaft  53  includes a base circle  53   a  which encompasses the region between the ends of arrow  53   b ; however, in other examples, the base circle may extend further or less than indicated by arrow  53   b  depending on the camshaft design. Exhaust camshaft  53  provides zero lift to exhaust valve  54  when exhaust valve  54  is in mechanical communication with base circle  53   a . Camshaft lobe  250  includes ramps  53   c  that span the region indicated by arrows  53   d . Camshaft lobe  250  also includes a nose  53   e  that spans the region indicated by arrow  53   f . Camshaft lobe  250  provides lift to exhaust valve  54  when ramps  53   c  or nose  53   e  are in mechanical communication with exhaust valve  54 . In some examples, a tappet or hydraulic lifter may be positioned between exhaust camshaft  53  and exhaust valve  54 . 
     Exhaust valve locking device  60  is shown in its base position where protrusions  208  and  210  are shown in their respective vertical and horizontal positions. Spring  212  provides a force to rotate shaft  214  and protrusions  208  and  210  to their base positions when cam lobe  250  is not in mechanical contact with protrusion  210  as shown. 
     Referring now to  FIG. 2B , an unlocked view of the exhaust valve locking mechanism of  FIG. 2A  is shown. The components shown in  FIG. 2B  that have the same reference numbers as the components shown in  FIG. 2A  are the same devices and operate in a same way. 
       FIG. 2B  shows cam lobe ramp  53   c  in mechanical contact with protrusion  210  as exhaust camshaft  53  rotates in a clockwise direction in this example. Contact between cam lobe ramp  53   c  and protrusion  210  causes protrusion  210  to rotate in a counter clockwise direction about shaft  214 . As a result, protrusion  208  rotates in a counter clockwise direction away from exhaust valve  54  so that pawl  204  is extracted from groove  220  via link  206 , thereby unlocking exhaust valve  54  which allows exhaust valve  54  to move downward in the  FIG. 2B  label direction. 
     In this way, cam lobe  250  provides mechanical force to overcome spring  212  so that exhaust valve  54  may be unlocked. Thus, exhaust valve locking device  60  is completely mechanically driven and operated. 
     Referring now to  FIG. 2C , a second unlocked view of the exhaust valve locking mechanism of  FIG. 2A  is shown. The components shown in  FIG. 2C  that have the same reference numbers as the components shown in  FIG. 2A  are the same devices and operate in a same way. 
       FIG. 2C  shows cam lobe nose  53   e  in mechanical contact with exhaust valve  54  and cam lobe ramp  53   c  is shown in mechanical communication with protrusion  210  as exhaust camshaft  53  rotates in a clockwise direction in this example. Contact between cam lobe ramp  53   c  and protrusion  210  keeps pawl  204  retracted as nose  53   e  lifts exhaust valve  54  so that exhaust valve  54  remains unlocked. 
     In this way, cam lobe  250  provides mechanical force to extract pawl  204  from exhaust valve  54  while exhaust valve  54  is being lifted. Further, pawl  204  remains extracted until valve  54  is in contact with base circle  53   a  so that there in not interference between pawl  204  and exhaust valve  54  while exhaust valve  54  is being lifted by camshaft  53 . 
     Referring now to  FIG. 2D , a plan view of pawl  204  is shown. Pawl  204  includes a U shaped slot  295  that allows pawl  204  to wrap around cylindrical land  221 . Slot  295  allows pawl  204  to engage exhaust valve  54  at groove  220  without contacting cylindrical land  221 . 
     Referring now to  FIG. 3A , an alternative exhaust valve locking device  60  is shown. The components shown in  FIG. 3A  that have the same reference numbers as the components shown in  FIG. 2A  are the same devices and operate in a same way. 
     Exhaust valve  54  is shown with exhaust valve locking device  60  shown in a position where exhaust valve  54  is locked closed. Pawl  204  engages groove  220  when electrically operated solenoid  302  is not energized for normally locked configurations. Alternatively, pawl  204  may be disengaged from groove  220  when electrically operated solenoid is deactivated for normally unlocked configurations. Electrically operated solenoid  302  may be operated via controller  12 . Spring  304  returns pawl  204  and shaft  303  to their base positions when exhaust valve  54  is in mechanical contact with base circle  53   a  and when electrically operated solenoid  302  is deactivated or de-energized for normally locked configurations. 
     Electrically operated solenoid  302  is commanded off or de-energized when exhaust valve  54  is in mechanical contact with base circle  53   a . Solenoid  302  is activated shortly before exhaust valve  54  is in mechanical contact with cam lobe ramp  53   c.    
     Referring now to  FIG. 3B , exhaust valve locking device  60  is shown in an unlocked position which allows camshaft lobe  250  to lift and open exhaust valve  54 . Exhaust gases may evacuate the engine cylinder when exhaust valve  54  is lifted. Upper shaft  201   b  is shown in mechanical contact with ramp  53   c . Pawl  204  is disengaged from groove  220 . Spring  304  is compressed and providing force to shaft  303 . However, electrically operated solenoid  302  is activated and it overcomes the force applied by spring  304  to shaft  303 . Exhaust valve  54  is shown partially lifted. 
     Referring now to  FIG. 3C , exhaust valve locking device  60  is shown in an unlocked position which allows camshaft lobe  250  to fully lift and open exhaust valve  54 . Exhaust gases may evacuate the engine cylinder when exhaust valve  54  is fully lifted. Upper shaft  201   b  is shown in mechanical contact with ramp  53   c . Pawl  204  is disengaged from groove  220 . Spring  304  is compressed and it provides a force to shaft  303 . Electrically operated solenoid  302  is activated and it overcomes the force applied by spring  304  to shaft  303  so that pawl  204  is not engaged. Exhaust valve  54  is shown fully lifted. 
     Thus, electrically operated solenoid may be operated to remove pawl  204  from exhaust valve  54  once for each rotation of exhaust camshaft  53 . Electrically operated solenoid may be deactivated to install pawl  204  into exhaust valve  54  once for each rotation of exhaust camshaft  53 . The groove  220  allows exhaust valve  54  to rotate during operation even though pawl  204  is engaged so that valve seating may be tight. 
     Referring now to  FIG. 4A , a locked view of another example exhaust valve locking mechanism  60  is shown. The components shown in  FIG. 4A  that have the same reference numbers as the components shown in  FIG. 2A  are the same devices and operate in a same way. 
     Exhaust valve locking mechanism  60  is shown in a base locked position in  FIG. 4A . Ramp  53   c  is not engaging protrusion  210  so pawl  404  is below wedge  402  which keeps exhaust valve  454  locked in a closed position. Exhaust valve  454  is in mechanical contact with base circle  53   a  of exhaust camshaft  53 . If exhaust gases impinge on a back side of exhaust valve  454 , wedge  402  encounters pawl  404  to limit motion of exhaust valve  454 . Pawl  404  is supported by structure (not shown) of cylinder head  35  shown in  FIG. 1  to support exhaust valve  454  when pawl  404  is engaged under wedge  402  as shown. 
     Referring now to  FIG. 4B , an unlocked view of the exhaust valve locking mechanism  60  of  FIG. 4A  is shown. The components shown in  FIG. 4B  that have the same reference numbers as the components shown in  FIG. 2A  are the same devices and operate in a same way. 
     Ramp  53   c  of camshaft lobe  250  is shown in mechanical contact with protrusion  210 . Camshaft lobe  250  causes protrusions  210  and  208  to rotate about shaft  214  as exhaust camshaft  53  rotates. Pawl  404  is shown withdrawn past the edge  403 , the slope or angle of wedge  402  and the force of cam lobe  250  acting on exhaust valve  454  may also act to push pawl  404  away from exhaust valve  454  to facilitate unlocking exhaust valve  454 . Exhaust valve  454  is also shown in mechanical contact with ramp  53   c  of camshaft lobe  250 , which lifts exhaust valve  454  from the valve seat (not shown). 
     In this way, camshaft lobe  250  provides force to unlock exhaust valve locking mechanism  60  and lift exhaust valve  454 . Exhaust camshaft  53  rotates clockwise causing protrusions  210  and  208  to rotate counter clockwise. Spring  212  rotates protrusions  210  and  208  counter clockwise after camshaft lobe  250  passes by protrusion  210 . 
     Referring now to  FIG. 4C , a side profile of exhaust valve  454  is shown. In this view, wedge  402  is shown extending from a side of exhaust valve  454 . Pawl  404  may take the form of a rectangular protrusion in this example. 
     Thus, the system of  FIGS. 1-4C  provides for an engine system, comprising: an engine including an exhaust valve; a camshaft including a cam lobe, the camshaft in mechanical communication with the exhaust valve; and an exhaust valve locking device in selective mechanical communication with the camshaft, the exhaust valve locking device in a position unlocking the exhaust valve when a ramp of the cam lobe is in contact with the exhaust valve locking device. The engine system includes where the exhaust valve locking device is in a base position when not in contact with the ramp of the cam lobe, and where the base position is a position of the exhaust valve locking device that locks the exhaust valve closed. The engine system further comprises a return spring, the return spring in mechanical communication with the exhaust valve locking device. 
     In some examples, the engine system includes where the exhaust valve locking device includes a C shaped locking pawl. The engine system includes where the exhaust valve locking device is configured to rotate. The engine system includes where the exhaust valve locking device includes a shaft and two protrusions extending from the shaft. The engine system further comprises a controller including non-transitory instructions stored in memory to deactivate a cylinder in response to degradation of the exhaust valve locking device. The engine system includes where deactivating the cylinder includes ceasing to supply fuel to the cylinder. 
     In some examples, the system comprises: an engine including an exhaust valve, a camshaft, and a camshaft lobe; and an exhaust valve locking device in selective mechanical communication with the exhaust valve, the exhaust valve locking device entering a groove in the exhaust valve when the exhaust valve is in mechanical communication with a base circle of the camshaft lobe. The system further comprises a solenoid, the solenoid in mechanical communication with the exhaust valve locking device. The system further comprises a controller and instructions to move the exhaust valve locking device in and out of the groove. The system includes where the exhaust valve locking device is operated via the camshaft lobe. The system includes where the exhaust valve locking device is in a base position when not in contact with a ramp of the camshaft lobe, and where the base position is a position of the exhaust valve locking device that locks the exhaust valve closed so that air flow through the cylinder is reduced or prevented. The system includes where the exhaust valve locking device includes a shaft and two protrusions extending from the shaft. 
     Referring now to  FIG. 5 , a prophetic sequence for operating an exhaust valve locking mechanism for an engine cylinder is shown. The sequence includes three plots that are aligned with engine crankshaft position and occur at the same time. The sequence may be provided by the system of  FIGS. 1-4C  according to the methods of  FIGS. 6 and 7 . 
     The first plot from the top of  FIG. 5  is a plot of exhaust camshaft lift versus engine crankshaft position. The vertical axis represents exhaust camshaft lift and exhaust valve opening amount increase in the direction of the vertical axis arrow. The horizontal axis represents crankshaft position and crankshaft degrees are marked along the horizontal axis. A crankshaft position of zero degrees represents top-dead-center compression stroke for the cylinder shown. 
     The second plot from the top of  FIG. 5  is a plot of a control solenoid command versus engine crankshaft position. The control solenoid command is issued by a controller to an exhaust valve locking mechanism control solenoid (e.g.,  302  of  FIG. 3A ). The exhaust valve locking mechanism control solenoid is commanded to unlock the exhaust valve locking mechanism when the trace is at a higher level near the vertical axis arrow. The exhaust valve locking mechanism control solenoid is commanded to lock the exhaust valve locking mechanism when the trace is at a lower level near the horizontal axis arrow. The horizontal axis represents crankshaft position and crankshaft degrees are marked along the horizontal axis. 
     The third plot from the top of  FIG. 5  is a plot of exhaust valve locking mechanism latch state versus engine crankshaft position. The exhaust valve locking mechanism is locked when the trace is at a higher level near the vertical axis arrow. The exhaust valve locking mechanism is not locked when the trace is at a lower level near the horizontal axis. The horizontal axis represents crankshaft position and crankshaft degrees are marked along the horizontal axis. 
     At crankshaft position C 0 , the exhaust camshaft lift is zero and the exhaust valve locking mechanism control solenoid is commanded locked. The exhaust valve locking mechanism latch state is at a high level to indicate that the exhaust valve of the cylinder is locked. By locking the exhaust valve, it may be less probable that the exhaust valve will open due to higher exhaust pressures. 
     At crankshaft angle C 1 , the exhaust camshaft lift is zero and the exhaust valve locking mechanism control solenoid is commanded unlocked. The exhaust valve locking mechanism is commanded unlocked before the exhaust camshaft begins to lift the exhaust valve so that the solenoid has time to energize and remove the pawl from the exhaust valve. The exhaust valve locking mechanism latch state is at a high level to indicate that the exhaust valve of the cylinder is locked at the time the exhaust valve locking mechanism is commanded unlocked. 
     At crankshaft angle C 2 , the exhaust camshaft lift is still zero and the exhaust valve locking mechanism control solenoid is still commanded unlocked. The exhaust valve locking mechanism latch state is at a low level to indicate that the exhaust valve of the cylinder is unlocked. Thus, the exhaust valve locking mechanism is commanded unlocked before the exhaust valve cam begins to provide lift to the exhaust valve. 
     Between crankshaft angle C 2  and crankshaft angle C 3 , the exhaust camshaft lift increases to lift the exhaust valve and then decreases to close the exhaust valve. The exhaust valve locking mechanism control solenoid is commanded unlocked and the exhaust valve locking mechanism is unlatched and unlocked. 
     At crankshaft angle C 3 , the exhaust camshaft lift is zero and the exhaust valve locking mechanism control solenoid is commanded off to lock the exhaust valve. The exhaust valve locking mechanism latch state is shown at a low level to indicate that the exhaust valve is not locked. 
     At crankshaft angle C 4 , the exhaust camshaft lift is zero and the exhaust valve locking mechanism control solenoid is still commanded off to lock the exhaust valve. The exhaust valve locking mechanism latch state is shown at a higher level to indicate that the exhaust valve is locked. The exhaust valve remains in a locked state until the sequence begins again at crankshaft angle C 5 . In this way, the exhaust valve locking mechanism control solenoid may be commanded at engine crankshaft angles to unlock a locked exhaust valve. 
     Referring now to  FIG. 6 , a flowchart of a method for operating an exhaust valve is shown. The method of  FIG. 6  may be included in the system of  FIGS. 1-4C . The method of  FIG. 6  may include physical actions taken by a controller and/or various actuators to transform operating states of an engine. 
     At  602 , method  600  retracts an exhaust valve locking mechanism to unlock a locked exhaust valve before the exhaust valve begins to open. The locking mechanism may be as illustrated in  FIGS. 2A-4C  or a similar design. The exhaust valve locking mechanism may be mechanically retracted or unlocked via one or more cam lobes operating on an exhaust valve locking mechanism. Alternatively, the exhaust valve locking mechanism may be unlocked via an electromechanical device (e.g., a solenoid). If the exhaust valve locking mechanism is unlocked via an electromechanical device, the electromechanical device may be operated based on engine crankshaft position. The exhaust valve locking mechanism unlocks the exhaust valve before the exhaust valve is not in mechanical communication with a base circle of a cam lobe operating the exhaust valve. In other words, the exhaust valve locking mechanism is unlocked while the exhaust valve is in contact or mechanical communication with a base circle of the exhaust cam lobe. For example, the exhaust valve locking mechanism is unlocked while the exhaust valve is in mechanical communication with a base circle of the exhaust cam lobe before the exhaust valve is in mechanical communication with the exhaust cam lobe ramp. Method  600  proceeds to  604 . 
     At  604 , method  600  closes the exhaust valve locking mechanism after the exhaust valve cam lobe ramp is in mechanical communication with the exhaust valve while the exhaust valve cam lobe base circle is in mechanical communication with the exhaust valve. Closing the exhaust valve locking mechanism locks the exhaust valve in a closed state. Method  600  proceeds to  606 . 
     At  606 , method  600  holds the exhaust valve locking mechanism in a position that locks the exhaust valve closed while the exhaust valve is in mechanical communication with a base circle of the exhaust camshaft lobe (e.g., the exhaust valve is in direct or indirect contact with the exhaust cam lobe base circle, but the contact or mechanical communication is not through the exhaust cam lobe itself). By locking the exhaust valve in a closed state while the exhaust valve is in mechanical communication with the base circle of the exhaust camshaft lobe, undesirable exhaust valve opening may be prevented. 
     Referring now to  FIG. 7 , a flowchart of a method for detecting exhaust valve locking mechanism degradation for a cylinder is shown. The method of  FIG. 7  may be included in the system of  FIGS. 1-4C . The method of  FIG. 7  may include physical actions taken by a controller and/or various actuators to transform operating states of an engine. The method of  FIG. 7  may be repeated for every engine cylinder that includes an exhaust valve locking mechanism. 
     At  702 , method  700  judges if there has been a misfire in the cylinder with the exhaust valve deactivating mechanism during a last or immediately previous cycle of the cylinder. A misfire may be detected via a reduction in crankshaft acceleration, cylinder pressure, or other known method. If method  700  judges that the cylinder with the exhaust valve locking mechanism experienced a misfire, the answer is yes and method  700  proceeds to  720 . Otherwise, the answer is no and method  700  proceeds to  704 . 
     At  720 , method  700  ceases to deliver fuel to the cylinder that experienced the misfire. The misfire may be related to degradation of the valve deactivating mechanism so the cylinder with the valve deactivating mechanism is deactivated via ceasing to supply fuel to the cylinder for one or more cylinder cycles (e.g., two engine revolutions). Method  700  proceeds to  704  after fuel flow is ceased to the cylinder for the present cylinder cycle. 
     Between  702  and  712 , combustion of air and fuel may be initiated in the cylinder if fuel flow to the cylinder is not deactivated at  720 . Thus, if misfire has not occurred in the cylinder during the immediately previous cycle of the cylinder, combustion may continue in the cylinder. However, if misfire is detected during the immediately previous cycle of the cylinder, combustion in the cylinder is prevented by ceasing to supply fuel to the cylinder. 
     At  704 , method  700  determines camshaft position. The camshaft position is determined via a camshaft position sensor. Additionally, the engine crankshaft position may be determined. One camshaft rotation is performed every two crankshaft revolution. Thus, one camshaft degree corresponds to two crankshaft degrees. Method  700  proceeds to  708  after camshaft position is determined. 
     At  708 , method  700  estimates the amount of time between commanding the valve locking mechanism to unlock the exhaust valve and the time the exhaust valve is unlocked. If the exhaust valve locking mechanism is unlocked via the camshaft lobe, the amount of time to open the exhaust valve lock may be made a value of zero or the amount of time it takes the engine to rotate through the crankshaft angle that unlocks the exhaust valve locking mechanism. If the exhaust valve locking mechanism is unlocked via a solenoid, the time to unlock the exhaust valve locking mechanism may be retrieved from a location in memory that holds an empirically determined value of time to unlock the exhaust valve locking mechanism. Method  700  proceeds to  710 . 
     At  710 , method  700  determines an actual total number of camshaft or crankshaft degrees at the present engine speed to unlock the exhaust valve locking mechanism. In one example, the amount of time to unlock the exhaust valve locking mechanism in seconds determined at  708  is multiplied by the engine speed in camshaft degrees per second to determine the total actual number of camshaft degrees it takes to open the exhaust valve locking device. Method  700  proceeds to  712 . 
     At  712 , method  700  commands the exhaust valve locking device to unlock. In one example, the exhaust valve locking device is commanded to open at a camshaft angle that corresponds to a camshaft angle where the base circle of the exhaust cam lobe ends and the ramp of the exhaust cam lobe begins plus the actual total number of camshaft degrees to unlock the exhaust valve locking mechanism as determined at  710  plus a predetermined actual total number of camshaft degrees for error margin. The actual total number of camshaft degrees to unlock the exhaust valve locking mechanism plus the actual total number of camshaft degrees for error margin moves the exhaust valve locking device command to a camshaft angle that corresponds to a camshaft angle where the base circle of the exhaust cam lobe for the cylinder is in mechanical communication with the exhaust valve. For example, if the base circle ends at 160 crankshaft degrees after top-dead-center compression stroke for the cylinder, the crankshaft margin is 10 crankshaft degrees, and the exhaust valve locking device unlocks in 5 crankshaft degrees at the present engine speed, the exhaust valve locking device is commanded unlocked at 145 crankshaft degrees after top-dead-center compression stroke for the cylinder. Method  700  proceeds to  714 . If the exhaust valve locking mechanism is operated via the camshaft lobe, method  700  proceeds to  714 . 
     At  714 , method  700  commands the exhaust valve locking mechanism closed at the engine crankshaft angle or camshaft angle where the exhaust valve closes (e.g., the camshaft angle where the camshaft lobe ramp ends and the camshaft lobe base circle begins). Method  700  proceeds to  716 . If the exhaust valve locking mechanism is operated via the camshaft lobe, method  700  proceeds to  716 . 
     At  716 , method  700  judges if there has been a misfire in the cylinder with the exhaust valve deactivating mechanism during a last or immediately previous cycle of the cylinder (same cylinder cycle as evaluated at  702 ). If method  700  judges that the cylinder with the exhaust valve locking mechanism experienced a misfire, the answer is yes and method  700  proceeds to  730 . Otherwise, the answer is no and method  700  proceeds to exit. 
     At  730 , method  700  judges if there is excess air in the engine&#39;s exhaust system. Excess air may be present if the exhaust valve opened to allow air inducted to the cylinder to be expelled without combustion having occurred in the cylinder. If excess air is detected in engine exhaust, the answer is yes and method  700  proceeds to  734 . Otherwise, the answer is no and method  700  proceeds to  732 . 
     At  732 , method  700  deactivates the cylinder and provides an indication of exhaust valve degradation. The cylinder may be deactivated via continuing to cease to supply fuel to the cylinder. An indication of valve degradation may be provided via displaying exhaust degradation on a user interface. Because excess air was not found in the exhaust gas, it may be determined that the exhaust valve remained in a locked state, thereby reducing air flow through the cylinder. Method  700  proceeds to exit. 
     At  734 , method  700  reduces an amount of exhaust gas recirculation (EGR) provided to the cylinder and increases an ignition coil charging time via increasing a dwell time for an ignition coil. By reducing EGR and increasing dwell time, it may be possible to reduce the possibility of engine misfire due to high EGR or lean air-fuel mixtures. Thus, because excess air was detected in the exhaust gases, it may be determined that the exhaust valve opened and closed. The opening and closing exhaust valve allows air to flow through the cylinder without being combusted since fuel flow to the cylinder is deactivated at  720 . 
     In this way, method  700  may judge if exhaust valve degradation is present. If exhaust valve degradation is determined, the cylinder may be deactivated. Otherwise, the exhaust valve is allowed to continue to operate and spark energy and EGR amount are adjusted to reduce the possibility of engine misfire. 
     Thus, the methods of  FIGS. 6 and 7  provide for an engine operating method, comprising: locking an exhaust valve of a cylinder in a closed position via a mechanism other than a valve spring in response to the exhaust valve being in mechanical communication with a base circle of a camshaft lobe. The method further comprises commanding unlocking the exhaust valve in response to the exhaust valve being in mechanical communication with a ramp of the camshaft lobe. The method further comprises deactivating a cylinder in response to a misfire in the cylinder after the exhaust valve was commanded unlocked. The method includes where the exhaust valve is commanded unlocked via the camshaft lobe. The method includes where the locking of the exhaust valve includes limiting motion of the exhaust valve via a spring return locking mechanism. The method includes where the locking of the exhaust valve is performed via a device that allows rotation of the exhaust valve. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, at least a portion of the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the control system. The control actions may also transform the operating state of one or more sensors or actuators in the physical world when the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with one or more controllers. 
     This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the description. For example, I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.