Abstract:
An internal combustion engine includes a valvetrain having a rocker arm assembly including a rocker arm on which a latch pin is mounted. An actuator for the latch pin, including an electromagnet, is mounted separately from the rocker arm. Therefore, the rocker arm is able to move independently from the electromagnet. The electromagnet is operative to cause the latch pin to actuate through magnetic flux following a magnetic circuit that passes through the rocker arm. Mounting the electromagnet apart from the rocker arm allows wires powering the electromagnet to be held in relatively static positions. The magnetic circuit is arranged to bring magnetic flux into the latch pin, or a co-acting part, within the volume of the rocker arm. This enables a compact design that is suitable for installation in engines where the available space under the valve cover may be very limited.

Description:
FIELD 
       [0001]    The present teachings relate to valvetrains, particularly valvetrains providing variable valve lift (VVL) or cylinder deactivation (CDA). 
       BACKGROUND 
       [0002]    Hydraulically actuated latches are used on some rocker arm assemblies to implement variable valve lift (VVL) or cylinder deactivation (CDA). For example, some switching roller finger followers (SRFF) use hydraulically actuated latches. In these systems, pressurized oil from an oil pump may be used for latch actuation. The flow of pressurized oil may be regulated by an oil control valve (OCV) under the supervision of an Engine Control Unit (ECU). A separate feed from the same source provides oil for hydraulic lash adjustment. This means that each rocker arm has two hydraulic feeds, which entails a degree of complexity and equipment cost. The oil demands of these hydraulic feeds may approach the limits of existing supply systems. In addition, there is a need to provide on board diagnostic information for cylinder deactivating and switching rocker arm assemblies. 
       SUMMARY 
       [0003]    The present teachings relate to a valvetrain suitable for an internal combustion engine that includes a combustion chamber, a moveable valve having a seat formed within the combustion chamber, and a camshaft. The valvetrain includes a rocker arm assembly that has a rocker arm and a cam follower configured to engage a cam on the camshaft as the camshaft rotates. In the present teachings, the valvetrain further includes a latch assembly. The latch assembly includes a latch pin mounted on the rocker arm and an actuator. The actuator includes an electromagnet. The actuator parts are mounted on components distinct from the rocker arm, whereby the rocker arm with the latch pin mounted to it has a freedom of movement independent from the electromagnet. The actuator is operative on the latch pin through magnetic force and does not require a mechanical interface with the latch pin. 
         [0004]    The latch pin is moveable between first and second positions. The electromagnet is operable to cause the latch pin to translate between the first and second positions. One of the first and second latch pin positions may provide a configuration in which the rocker arm assembly is operative to actuate the moveable valve in response to rotation of the camshaft to produce a first valve lift profile. The other latch pin position may provide a configuration in which the rocker arm assembly is operative to actuate the moveable valve in response to rotation of the camshaft to produce a second valve lift profile, which is distinct from the first valve lift profile, or the moveable valve may be deactivated. 
         [0005]    Using electromechanical latch assemblies instead of hydraulically-actuated latches can reduce complexity and demands for oil in some valvetrain systems. Mounting the electromagnet on a part that is distinct from the rocker arm avoids running wires to the rocker arm. Rocker arms reciprocate rapidly over a prolonged period and in proximity to other moving parts. Wires attaching to a rocker arm could be caught, clipped, or fatigued and consequently short out. 
         [0006]    According to some aspects of the present teachings, the electromagnet is operative to cause the latch pin to translate between the first and second positions through magnetic flux following a magnetic circuit that passes through the actuator and the rocker arm. In some of these teachings, the magnetic circuit also passes through the latch pin. In an alternative teaching, rather than passing through the latch pin, the magnetic circuit passes through another part that is mounted on the rocker arm and is positioned to act against the latch pin. The magnetic flux may be generated by the electromagnet and/or one or more permanent magnets. In some of these teachings, the electromagnet is operative to actuate the latch pin by generating, or ceasing to generate, the flux. In some of these teachings, the electromagnet is operative to actuate the latch pin by diverting the flux. Structuring the latch assembly to make the actuator operable through a magnetic circuit that brings magnetic flux into the latch pin or a co-acting part within the rocker arm enables the latch assembly to have a compact design suitable for packaging within the limited space available under a valve cover. 
         [0007]    According to some aspects of the present teachings, the electromagnet is mounted in a position such that a line oriented in the direction along which the latch pin translates between its first and second positions and passing through the latch pin while the cam is on base circle will not intersect the electromagnet or the space it encircles. This condition may be satisfied regardless of the cam position and characterizes a freedom of electromagnet positioning enabled by applying a magnetic circuit concept according to the present teachings. In some of these teachings, a load-bearing member of the valvetrain completes the magnetic circuit. 
         [0008]    In some of these teachings, the electromagnet, a permanent magnet, or a combination of one or more electromagnets and permanent magnets are positioned and functional to provide a magnetic field effective to hold the latch pin in at least one of the first and second positions through magnetic flux that follows the magnetic circuit. In some of these teachings, the electromagnet is operable to alter the magnetic flux in the circuit and thereby cause the latch pin to translate between the first and second positions. 
         [0009]    In some of these teachings, the actuator is operative to change a magnetic force on the latch pin or an abutting part mounted on the rocker arm. In some of these teachings, the actuator is operative to change a magnetic force on the latch pin. The part on which the magnetic force acts is magnetized. The change in magnetic force may include the application of the magnetic force or the removal of the magnetic force. In some of these teachings, the change in magnetic force includes a reversal of a direction in which magnetic force acts on the part. 
         [0010]    In some of these teachings, the magnetic circuit includes the latch pin or an abutting part mounted on the rocker arm. In some of these teaching, the magnetic circuit includes the latch pin. In some of these teaching, all or a portion of the part included in the magnetic circuit is formed of a magnetically susceptible material that if replaced with aluminum would render the electromagnet inoperative to cause the latch pin to translate between the first and second positions. In some of these teachings, the magnetically susceptible material is a low coercivity ferromagnetic material. Making a permanent magnet a part of the latch pin could undesirably increase the weight of the latch pin. 
         [0011]    An operative portion of the magnetic flux may simply pass through the volume of the rocker arm. In some of these teachings, the magnetic circuit includes the structure of the rocker arm. All or part of the rocker arm may be formed of magnetically susceptible material. In some of these teachings, the rocker arm is formed primarily or entirely of low coercivity ferromagnetic material. In some of these teachings, the magnetic flux passes through a pole piece fixed to the core structure of the rocker arm. In some of these teachings, the rocker arm includes magnetically susceptible material that if replaced by aluminum would render the electromagnet inoperative to cause the latch pin to translate between the first and second positions. 
         [0012]    In some of these teachings, magnetic flux following the magnetic circuit in one of a forward and a reverse direction enters the latch pin crossing directly or across an air gap from a pole piece that is the rocker arm or is fixed to the rocker arm and leaves the latch pin crossing directly or across an air gap to a second pole piece. The second pole piece is not mounted on the rocker arm, whereby the rocker arm is operative to move independently from the second pole piece. In some of these teaching, the magnetic flux passes through the rocker arm to the latch pin and from the latch pin across a variable width air gap to a pole piece that is not mounted on the rocker arm. The width of the air gap varies as the latch pin translates between the first and second positions. In some of these teachings, the width of the air gap also varies as the rocker arm pivots during operation of the rocker arm assembly. The pole piece that is not mounted on the rocker arm may be in a fixed position relative to the electromagnet. The term pole piece as used herein may encompass any structure that completes a magnetic circuit regardless of the position of the pole piece within the magnetic circuit. The structures determining these flux paths relate to a compact design. In some of these teachings, the electromagnet includes a coil around a solid immovable core. That core may be considered a pole piece. 
         [0013]    In some of these teachings, the valvetrain is installed in an engine having a cylinder head and one or more parts including a valve cover that define the limits of an enclosed space underneath the valve cover. In some of these teachings, the parts of the engine along the shortest path between the latch pin and the nearest outer edge of that enclosed space consist essentially of one or more pole pieces that complete the magnetic circuit. The outer edge may be defined by the cylinder head. The latch pin may extend outward from the back of the rocker arm assembly and there may be only a relatively narrow gap between the rocker arm assembly and the cylinder head. The electromagnet may be too large to fit within that gap, however, the gap may accommodate a pole piece that may complete a magnetic circuit with the latch pin and the electromagnet. 
         [0014]    In some aspects of the present teachings, the magnetic flux passes through a pivot for the rocker arm assembly. The pivot may provide a fulcrum for the rocker arm. Passing the flux through the pivot may provide a pathway through which the flux may be brought close to the latch pin or a co-acting part at a location within the rocker arm. In some of these teachings, the magnetic flux passes through the structure of the pivot. In some of these teachings, the pivot structure forms part of a magnetic circuit through which the actuator operates such that replacing that structure with aluminum would render the electromagnet inoperative to cause the latch pin to translate between the first and second positions. In some of these teachings, the pivot is made primarily of low coercivity ferromagnetic material. In some of these teachings, the pivot is a lash adjuster. In some of these teachings, the pivot is a hydraulic lash adjuster. The pivot may be relatively stationary compared to the rocker arm and flux from the actuator may be transferred to the pivot relatively easily. In some of these teachings, the electromagnet is mounted to the pivot. This structure may facilitate packaging and allow a structure through which the electromagnet is mounted to also provide a pole piece for the magnetic circuit. 
         [0015]    In some aspects of the present teachings, there are two of the rocker arm assemblies and two of the latch pins and the electromagnet is operable to simultaneously cause both latch pins to translate between first and second positions. In some of these teachings, the two latch pins form parts of a single magnetic circuit for the electromagnet. In some of these teachings, the two rocker arm assemblies are side-by-side. In some of these teachings, the electromagnet is located between the two rocker arm assemblies. In some of these teachings, the electromagnet is mounted on a bracket supported by two lash adjusters, one associated with each of the two rocker arm assemblies. In some of these teachings, the magnetic circuit further includes two lash adjusters, one associated with each of the two rocker arm assemblies. In some of these teachings, the electromagnet is mounted on a bracket supported by four lash adjuster, each associated with a distinct rocker arm assembly. In some of these teachings, two lash adjusters to which the actuator is mounted are canted with respect to one another, whereby a mounting frame for the actuator that encircles both lash adjusters cannot slide freely upward and downward without interference. 
         [0016]    In some of the present teachings, the valvetrain is installed within an engine having a combustion chamber and the electromagnet of the actuator is mounted in a position that is fixed with respect to the combustion chamber. In some of these teachings, the electromagnet is mounted to a cylinder head, a cam carrier, a camshaft journal, or a valve cover of the engine. In some of these teachings, the electromagnet is mounted to the outer shell of one or more lash adjusters. Mounting the electromagnet to a part that is distinct from the rocker arm and that is not constrained to move with the rocker arm allows wires powering the electromagnet to be maintained in relatively static positions. 
         [0017]    In some of the present teachings, the actuator is operative to cause the latch pin to actuate through a magnetic field that crosses an air gap between the latch pin and an actuator part, which is a part that is not mounted on the rocker arm. In some of these teachings, the electromagnet is operative to generate the magnetic field. In some of these teachings, a permanent magnet generates the magnetic field. The actuator may be operative to redirect flux from the permanent magnet and thereby cause the latch pin to actuate. 
         [0018]    In some of the present teachings, the rocker arm assembly and the latch assembly are structured to stably maintain the latch pin position in each of its first and second positions independently from the electromagnet. Stabilizing forces may be provided by springs, by permanent magnets, or a combination of springs and permanent magnets. The actuator may be operative to actuate the latch pin either way between the first and the second position. In some of these teachings, the internal combustion engine has circuitry operable to energize the electromagnet with a DC current in either a first direction or a reverse of the first direction. The electromagnet powered with current in the first direction maybe operative to actuate the latch pin from the first position to the second position. The electromagnet powered with current in the reverse direction may be operative to actuate the latch pin from the second position to the first position. In some others of these teachings, the actuator includes two electromagnets, one for latching and the other for unlatching. The two electromagnets may have windings in opposite directions. 
         [0019]    In some of the present teachings, a permanent magnet is operative to stabilize the latch pin in both the first and second positions. In some of these teachings, the permanent magnet is mounted to the rocker arm. In some others of these teachings, the permanent magnet is part of the actuator. In some of these teachings, absent any magnetic fields generated by the electromagnet or other external sources, when the latch pin is in the first position, an operative portion of the magnetic flux from the permanent magnet follows a first magnetic circuit and when the latch pin is in the second position, an operative portion of the magnetic flux from the permanent magnet follows a second magnetic circuit distinct from the first magnetic circuit. The actuator may be operative to redirect the permanent magnet&#39;s flux away or toward one or the other of these magnetic circuits and thereby cause the latch pin to actuate. In some of these teachings redirecting the magnetic flux includes reversing the magnetic polarity in a low coercivity ferromagnetic element forming part of both the first and second magnetic circuits. A latch assembly operating with a flux-shifting mechanism may be made compact and thus more suitable for installation within an engine. 
         [0020]    In some of these teachings, at least one of the magnetic circuits passes through the actuator. A magnetic circuit passing through the actuator may facilitate actuation of the latch pin though operation of the electromagnet. In some of these teachings, the other circuit does not pass through the actuator. The circuit not passing through the electromagnet may be much shorter, have lower magnetic flux leakage, and allow the permanent magnet to apply a greater holding force to the latch pin. 
         [0021]    In some of these teachings, the latch assembly comprises two permanent magnets, both of which are operative to stabilize the latch pin in both the first and the second positions. The second permanent magnet may be mounted to the rocker arm or the actuator. When the latch pin is in the first position, an operative portion of the magnetic flux from the second permanent magnet follows a third magnetic circuit and when the latch pin is in the second position, an operative portion of the magnetic flux from the permanent magnet follows a fourth magnetic circuit distinct from the third magnetic circuit. The electromagnet may be operative to redirect the second permanent magnet&#39;s flux away or toward one or the other of these magnetic circuits and thereby cause the latch pin to actuate. In some of these teachings, one of the third and fourth circuits passes through the actuator and the other does not. In each of the latch pin positions, one of the active magnetic circuits may provide a short flux path that results in a high holding force on the latch pin and the other magnetic circuit may pass through the electromagnet and facilitate actuation of the latch pin though operation of the electromagnet. 
         [0022]    In some of the present teachings, the latch pin is mounted on a rocker arm of the rocker arm assembly and, along with the rocker arm, has a range of motion relative to the actuator. An air gap in a magnetic circuit through which the actuator operates on the latch pin may vary in width in conjunction with this relative motion. The rocker arm position and thus the air gap width may be affected at times by the position of the cam. In some of these teachings, the rocker arm assembly and the latch assembly are configured such that the actuator does not need to be operative on the latch pin except within a limited portion of rocker arm&#39;s range of motion. Actuation of the latch pin may occur only when the cam is on base circle. 
         [0023]    In some of these teachings, the rocker arm assembly is configured whereby the rocker arm to which the latch pin is mounted remains substantially stationary when the latch pin is in a non-engaging configuration. The engaging configuration may be maintained independently from the actuator. In some of these teachings, the engaging configuration is maintained by a spring. If the actuator need only be operative on the latch pin when the rocker arm is in one particular position, a structure providing a low reluctance magnetic circuit that enables the actuator&#39;s operability is more easily achieved. In some of these teachings, in the engaging configuration, with each cycle of the cam the rocker arm reaches a position in which the actuator is operative to induce a magnetic force on the latch pin sufficient to overcome the spring force and hold the latch pin in the non-engaging configuration. The actuator need not be so operative throughout the cam cycle. 
         [0024]    In some of the present teachings, the rocker arm to which the latch pin is mounted has a range of motion and the operability of the actuator is maintained throughout that range of motion by one or more sliding joints in the magnetic circuit. In some of these teachings, one part of the sliding magnetic joint is a pole piece held in a fixed position with respect to the actuator and the other is part of the latch pin. In some of these teachings, one part of the sliding magnetic joint is a pole piece held in a fixed position with respect to the actuator and the other is the rocker arm to which the latch pin is mounted or a pole piece fixed to that rocker arm. 
         [0025]    In some of the present teachings, first pole piece moves in conjunction with the rocker arm, a second pole piece remains stationary with respect to the actuator, and one of the first and second components has a surface extending along the direction in which the first component moves relative to the second component. This structure may form a sliding magnetic joint and allow the first and second components to remain proximate as the rocker arm travels through its range of motion. In some of these teachings, both pole pieces have surfaces extending along the direction of relative motion. Providing both pole pieces with surfaces extending along the direction of relative motion may maintain proximity between the two components and provide a large area through which magnetic flux may easily pass between them. 
         [0026]    In some of these teachings, the latch pin has a pole piece an outer portion of which traces an arc as the rocker arm moves through its range of motion and the actuator has a pole piece with a surface parallel to the arc and positioned to remain in proximity to the arc throughout the rocker arm&#39;s range of motion. The two components may form a sliding magnetic joint for the magnetic circuit. In some of these teachings, the actuator includes one or more pole pieces extending proximate a side of the rocker arm to form a sliding magnetic joint. In some of these teachings, the actuator includes a pole pieces extending proximate a side of the latch pin where the latch pin extends outward from the rocker arm. The effectiveness of the actuator may depend on its positioning relative to the rocker arm. The effect of variations in that positioning due to lash adjustment and manufacturing tolerances may be ameliorated by one or more sliding magnetic joints. 
         [0027]    In some of the present teachings, the latch pin is mounted to a first rocker arm and a second rocker arm passes between the first rocker arm and the actuator over the course of the second rocker arm&#39;s range of motion. Nevertheless, a magnetic circuit that passes between the actuator and the latch pin may be formed. Moreover, in some of these teachings, the magnetic circuit may be maintained and stabilize the latch pin position throughout the second rocker arm&#39;s range of motion. In some of these teachings, pole pieces are mounted to the second rocker arm that complete a magnetic circuit that includes the latch pin and the actuator. In some of these teachings, pole pieces mounted to either the actuator or the first rocker arm pass around the second rocker arm to complete the magnetic circuit. 
         [0028]    Some aspects of the present teachings provide a module for installation in an engine. The module includes a rocker arm assembly, a lash adjuster, and an actuator according to the present teachings. In some of these teachings, the lash adjuster is secured to the rocker arm assembly. The module may be convenient for installation in an engine and may facilitate correct positioning of the actuator relative to the rocker arm. A connecting piece that secures the lash adjuster to the rocker arm assembly prior to installation may be removed after installation. 
         [0029]    Some aspects of the present teachings relate to methods of operating an internal combustion engine. In some of these teachings, the engine includes a valvetrain in which a rocker arm assembly has a latch pin mounted to a rocker arm. The latch pin provides the rocker arm assembly with engaging and non-engaging configurations. According to some aspects of the present teachings, a method of operating the engine includes operating the engine with the latch pin in one of the engaging and non-engaging configurations. An electromagnet of an actuator that is mounted within the engine but on a component distinct from the rocker arm is energized to cause magnetic flux to pass through the rocker arm. The magnetic flux passing through the rocker arm causes the latch pin to translate and thereby changes the rocker arm assembly configuration. The engine is then further operated with the rocker arm assembly in the other of the engaging and non-engaging configurations. In some of these teaching, the latch pin is actuated by magnetic flux that passes through the structure of the rocker arm. In some of these teaching, the latch pin is actuated by magnetic flux that passes through the structure of a pivot that provides a fulcrum on which the rocker arm pivots. 
         [0030]    Some aspects of the present teachings relate to a method of operating an internal combustion engine in which an electrical circuit that includes an electromagnet operative to actuate a rocker arm-mounted latch pin is used to provide rocker arm position information. Rocker arm position may be related to camshaft position. Accordingly, the data may be interpreted to provide camshaft position information. The information may be used to perform an engine management or diagnostic operation. The method is applicable to an internal combustion engine that includes a combustion chamber, a moveable valve having a seat formed in the combustion chamber, a camshaft on which a cam is mounted, a rocker arm assembly including a rocker arm and a cam follower configured to engage the cam as the camshaft rotates, and a latch assembly including a latch pin mounted on the rocker arm and an actuator that includes an electromagnet. The actuator parts are need not be mounted on the rocker arm, whereby the rocker arm with the latch pin may move independently from the actuator. The electromagnet is operative to cause the latch pin to translate between the first and the second position through magnetic flux that follows a magnetic circuit that passes through the latch pin and includes an air gap between the latch pin and a pole piece of the actuator. The pole piece is mounted on a part distinct from the rocker arm. The rocker arm assembly and the latch assembly are structured such that the air gap varies in width in relation to a motion of the rocker arm that actuates the moveable valve. The method includes analyzing data relating to a current or voltage in an electrical circuit comprising the electromagnet to obtain rocker arm position information, and using the information in an operation. The data is obtained while the engine is operating and the camshaft is rotating. Analyzing the data may also provide latch pin position information, which may also be used in an engine management or diagnostic operation. 
         [0031]    In some of these teachings, the rocker arm or cam shaft position information is used to manage the engine. Managing the engine may include regulating an ignition timing or a fueling event. In some of these teachings, the latch assembly replaces a cam position sensor in engine management operations. In some of these teachings, two or more of the latch assemblies are used to serve the purpose a cam position sensor. Obtaining data from more than one latch assembly allows for a more accurate determination of cam position. 
         [0032]    In some of these teachings, the information is used to perform a diagnostic. Performing a diagnostic may include reporting a diagnostic result. In some of these teachings, if the rocker arm assembly is operating correctly, the rocker arm on which the latch pin is mounted will go through a first range of motion if the latch pin is in the engaging position and remain stationary or go through a second range of motion that is distinct from the first if the latch pin is in the non-engaging position. The air gap width will depend on the rocker arm position. As the air gap varies in width, the magnetic reluctance of the magnetic circuit and the inductance of the electromagnet will also vary. The inductance will be reflected in the current or voltage data, allowing the rocker arm position to be determined. In some of these teachings, the data over a span of time is analyzed to diagnose rocker arm motion. These methods allow the same electromagnet that is used to actuate the latch pin to also provide on-board diagnostic (OBD) information or to be used for engine management. 
         [0033]    In some of these teachings, a circuit including the electromagnet is powered to facilitate gathering the data used to obtain rocker arm position information. In some of these teachings, the electrical circuit is given a pulse insufficient to actuate the latch pin and the data relates to a current or voltage induced by the pulse. In some of these teachings, gathering the data comprises gathering the data over a cam cycle through which the electrical circuit is continuously powered with a current that does not maintain or affect the latch pin position. In some of these teachings, the electromagnet is powered with a DC current to actuate the latch pin and is powered with an AC current while gathering the data. The AC current need not affect the latch pin position. The AC signal may be driven on top of the DC current. 
         [0034]    In some of these teachings, the information is used to determine whether an event referred to as a “critical shift” has occurred. A critical shift is an event in which a latch pin slips out of engagement while the cam is lifting a rocker arm. When this happens, the rocker arm to which the latch pin is mounted rapidly returns to the position normally associated with base circle. A time variation of a current within the circuit comprising the electromagnet or an absolute value of that current at a particular time may be used to determine whether a critical shift has taken place. 
         [0035]    A method in accordance with some other aspects of the present teachings relates to the case in which the latch pin is stable in both engaging and non-engaging positions. In this method, the engine is operated while using a permanent magnet to maintain the latch pin in the engaging position. An electromagnet that is mounted on a part distinct from the rocker arm is energized to redirect magnetic flux from the magnet and cause the latch pin to switch to a non-engaging position. The engine is then further operated with the permanent magnet maintaining the latch pin in the non-engaging position. In some of these teachings, the electromagnet is subsequently energized with a current in the reverse direction to again redirect the magnetic flux from the magnet and cause the latch pin to switch back to the engaging position. 
         [0036]    In some of the present teachings, the rocker arm to which the latch pin is mounted is of a design that was put into production for use with a hydraulically actuated latch. In some of these teachings, the rocker arm to which the latch pin is mounted includes a hydraulic chamber adapted to receive a hydraulically actuated latch pin. In some of these teachings, a magnetically actuated latch pin is installed in that hydraulic chamber. Rocker arms for commercial applications are typically manufactured using customized casting and stamping equipment requiring a large capital investment. The present disclosure provides designs that allow these same rocker arms to be used with a magnetically actuated latch pin. 
         [0037]    Some aspects of the present teachings relate to a method of retrofitting for electromagnetic latching a rocker arm manufactured for hydraulic latching. The method includes installing a latch pin within a hydraulic chamber of the rocker arm with a portion of the latch pin protruding from the chamber. The rocker arm is installed within an engine in a magnetic circuit in which flux from an electromagnet in one of a North to South or South to North direction will enter the latch pin through the rocker arm and leave the rocker arm across an air gap between the protruding portion of the latch pin and a pole piece of the latch assembly. 
         [0038]    The primary purpose of this summary has been to present certain of the inventors&#39; concepts in a simplified form to facilitate understanding of the more detailed description that follows. This summary is not a comprehensive description of every one of the inventors&#39; concepts or every combination of the inventors&#39; concepts that can be considered “invention”. Other concepts of the inventors will be conveyed to one of ordinary skill in the art by the following detailed description together with the drawings. The specifics disclosed herein may be generalized, narrowed, and combined in various ways with the ultimate statement of what the inventors claim as their invention being reserved for the claims that follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1A  is a partial cross-section of an internal combustion engine with a valvetrain according to some aspects of the present teachings. 
           [0040]      FIG. 1B  is the same view as  FIG. 1A , but with the latch pin moved from an engaging to a non-engaging position. 
           [0041]      FIG. 1C  is the same view as  FIG. 1A , but with the cam risen off base circle. 
           [0042]      FIG. 1D  is the same view as  FIG. 1B , but with the cam risen off base circle. 
           [0043]      FIG. 2A  provides a perspective view of a portion of the valvetrain of the engine illustrated by  FIG. 1A . 
           [0044]      FIG. 2B  provides the same view as  FIG. 2A , but with the latch pins moved from engaging to non-engaging positions. 
           [0045]      FIG. 3A  provides a perspective view of an actuator mounting frame according to some aspects of the present teachings, which is used in the valvetrain of  FIG. 2A . 
           [0046]      FIG. 3B  provides an explode view of the mounting frame of  FIG. 3A . 
           [0047]      FIG. 3C  provide a perspective view of four actuators  127 A according to the present teachings incorporating the mounting frame of  FIG. 3A . 
           [0048]      FIG. 4  provides a perspective view of a valvetrain according to some aspects of the present teachings with a pole piece shown in transparency. 
           [0049]      FIG. 5  is a partial cross-section of an internal combustion engine according to some aspects of the present teachings including a cross-section of the valvetrain of  FIG. 4  through one of the rocker arm assemblies of that valvetrain. 
           [0050]      FIG. 6  is a perspective view of an actuator used in the valvetrain of  FIG. 4 . 
           [0051]      FIG. 7  is a perspective view of a portion of the engine of  FIG. 5  showing some parts in transparency and illustrating a magnetic circuit according to some aspects of the present teachings. 
           [0052]      FIG. 8  is a flow chart of a method of operating an internal combustion engine according to some aspects of the present teachings. 
           [0053]      FIG. 9  is a flow chart of a diagnostic method according to some aspects of the present teachings. 
           [0054]      FIG. 10A  illustrates a latch assembly according to some aspects of the present teachings with the latch pin in a non-engaging position. 
           [0055]      FIG. 10B  illustrates the latch assembly of  FIG. 10A  with the latch pin in an engaging position. 
           [0056]      FIG. 11A  illustrates a cross-section along the line  11 - 11  of  FIG. 10B . 
           [0057]      FIG. 11B  illustrates the cross-section along the line  11 - 11  of  FIG. 10B  as it would appear after a cam has raised the rocker arm. 
           [0058]      FIG. 12A  illustrates a cross-section along the line  12 - 12  of  FIG. 10B . 
           [0059]      FIG. 12B  illustrates the cross-section along the line  12 - 12  of  FIG. 10B  as it would appear after a cam has raised the rocker arm. 
           [0060]      FIG. 13A  illustrates a cross-section along the line  13 - 13  of  FIG. 10B . 
           [0061]      FIG. 13B  illustrates the cross-section along the line  13 - 13  of  FIG. 10B  as it would appear after a cam has raised the rocker arm. 
           [0062]      FIG. 14A  illustrates a latch assembly according to some aspects of the present teachings with the latch pin in a non-engaging position. 
           [0063]      FIG. 14B  illustrates the latch assembly of  FIG. 14A  with the latch pin in an engaging position. 
           [0064]      FIG. 15A  illustrates a cross-section along the line  15 - 15  of  FIG. 14B . 
           [0065]      FIG. 15B  illustrates the cross-section along the line  15 - 15  of  FIG. 14B  as it would appear after a cam has raised the rocker arm. 
           [0066]      FIG. 16A  illustrates a cross-section along the line  16 - 16  of  FIG. 14B . 
           [0067]      FIG. 16B  illustrates the cross-section along the line  16 - 16  of  FIG. 14B  as it would appear after a cam has raised the rocker arm. 
           [0068]      FIG. 17A  illustrates a cross-section along the line  17 - 17  of  FIG. 14B . 
           [0069]      FIG. 17B  illustrates the cross-section along the line  17 - 17  of  FIG. 14B  as it would appear after a cam has raised the rocker arm. 
           [0070]      FIG. 18  is a flow chart of a method of operating an internal combustion engine in accordance with some aspects of the present disclosure. 
           [0071]      FIG. 19A  illustrates a latch assembly according to some aspects of the present teachings with the latch pin in an engaging position. 
           [0072]      FIG. 19B  illustrates the latch assembly of  FIG. 19A  with the latch pin in a non-engaging position. 
           [0073]      FIG. 20  is a top partial cutaway view of an internal combustion engine according to some other aspects of the present teachings 
           [0074]      FIG. 21A  provides a side view illustrating the relative positioning of the parts shown in region  400  of  FIG. 20 . 
           [0075]      FIG. 21B  provides a side view illustrating the relative positioning of the parts shown in  FIG. 20  after the cams rise off base circle with the latch pin in a non-engaging position. 
           [0076]      FIG. 21C  provides a side view illustrating the relative positioning of the parts shown in  FIG. 20  after the cams rise off base circle with the latch pin in an engaging position. 
           [0077]      FIG. 22  illustrates a modification of the valvetrain in  FIG. 1A  according to some aspects of the present teachings. 
       
    
    
     DETAILED DESCRIPTION 
       [0078]    In the drawings, some reference characters consist of a number followed by a letter. In this description and the claims that follow, a reference character consisting of that same number without a letter is equivalent to a listing of all reference characters used in the drawings and consisting of that same number followed by a letter. For example, “permanent magnet  200 ” is the same as “permanent magnet  200 A,  200 B,  200 C”. 
         [0079]      FIG. 1A  provides a partial-cutaway side view of a portion of an engine  100 A including a valvetrain  101 A in accordance with some aspects of the present. Engine  100 A includes a cylinder head  130  in which a combustion chamber  137  is formed, a moveable valve  185  having a seat  186  formed within combustion chamber  137 , and a camshaft  169  on which a cam  167  is mounted. Moveable valve  185  may be a poppet valve. Valvetrain  101 A includes rocker arm assembly  115 A, hydraulic lash adjuster (HLA)  181 , and latch assembly  105 A. Rocker arm assembly  115 A includes rocker arm  103 A (an outer arm) and rocker arm  103 B (an inner arm). HLA  181  is an example of a pivot. It provides a fulcrum on which rocker arm  103 A pivots. A pivot may alternatively be a mechanical lash adjuster, a post that provides a fulcrum on which a rocker arm pivots, or a rocker shaft. Outer arm  103 A and inner arm  1036  are pivotally connect through shaft  149 . A cam follower  107  may be mounted to inner arm  103 B through bearings  165  and shaft  147 . Cam follower  107  is configured to engage cam  167  as camshaft  169  rotates. Cam follower  107  is a roller follower but could alternatively be another type of cam follower such as a slider. 
         [0080]    Shaft  147  protrudes outward through openings  182  in the sides of outer arm  103 A where it engages torsion springs  145  (see  FIG. 2A ), which are mounted to outer arm  103 A. If inner arm  103 B pivots downward relative to outer arm  103 A on shaft  149  as shown in  FIG. 1  D, torsion springs  145  act on shaft  147  to drive inner arm  103 B to pivot back toward the position shown in  FIG. 1A . 
         [0081]    Latch assembly  105 A includes an actuator  127 A mounted to HLA  181  and a latch pin  114 A mounted on rocker arm  103 A. In this specification, the terms “latch pin” and “rocker arm” encompass the most basic structure that would be commonly understood as constituting a “latch pin” or a “rocker arm” and may further encompass parts that are rigid and rigidly held to that most basic structure. A rocker arm assembly is operative to form one or more force transmission pathways between a cam and a moveable valve. A rocker arm is a lever operative to transmits force from the cam along one or more of those pathways. The most basic structure of the rocker arm, which is its core structure, is capable of bearing the load and carrying out that function. 
         [0082]    Latch pin  114 A is translatable between a first position and a second position. The first position may be an engaging position, which is illustrated in  FIG. 1A . The second position may be a non-engaging position, which is illustrated in  FIG. 1B . A spring  141  mounted within outer arm  103 A may be configured to bias latch pin  114 A into the engaging position. When latch pin  114 A is in the engaging position, rocker arm assembly  115 A may be described as being in an engaging configuration. When latch pin  114 A is in the non-engaging position, rocker arm assembly  115 A may be described as being in a non-engaging configuration. 
         [0083]      FIG. 1C  shows the effect if cam  167  rises off of base circle while latch pin  114 A is in the engaging position. Latch pin  114 A may engage lip  109  of inner arm  103 B, after which inner arm  103 B and outer arm  103 A may be constrained to move in concert. HLA  181  may provide a fulcrum on which inner arm  103 B and outer arm  103 A pivot together as a unit, driving down on valve  185  via an elephant&#39;s foot  151 , compressing valve spring  183  against cylinder head  130 , and lifting valve  185  off its seat  186  within combustion chamber  137  with a valve lift profile determined by the shape of cam  167 . The valve lift profile is the shape of a plot showing the height by which valve  185  is lifted of its seat  186  as a function of angular position of camshaft  169 . 
         [0084]      FIG. 1D  shows the effect if cam  167  rises off of base circle while latch pin  114 A is in the non-engaging position. Cam  167  still drives inner arm  103 B downward, but instead of compressing valve spring  183 , inner arm  103 B pivots on shaft  149  against the resistance of torsion springs  145 . Torsion springs  145  yield more easily than valve spring  183 . Outer arm  103 A remains stationary and valve  185  remains on its seat  186 . Accordingly, the non-engaging configuration may provide deactivation of a cylinder with a port controlled by valve  185 . Alternatively, there may be additional cams that operate directly on outer arm  103 A. These additional cams may provide a lower valve lift profile than cam  167 . Therefore, the non-engaging configuration for rocker arm assembly  115 A may provide an alternate valve lift profile and rocker arm assembly  115 A may provide a switching rocker arm. 
         [0085]    Actuator  127 A may include an electromagnet  119  and pole pieces  131 A and  131 B. Actuator  127 A is mounted to HLA  181  through pole piece  131 A, which also provides a core for electromagnet  119 . HLA  181  includes an inner sleeve  175  and an outer sleeve  173 . Outer sleeve  173  is installed within a bore  174  formed in cylinder head  130 . Outer sleeve  173  may rotate within bore  174 , but is otherwise substantially stationary with respect to cylinder head  130 . Inner sleeve  175  is telescopically engaged within outer sleeve  173  and provides a fulcrum on which outer arm  103 A pivots. That fulcrum may be hydraulically raised or lowered to adjust lash. 
         [0086]    Latch pin  114 A, outer arm  103 A, inner sleeve  175 , and outer sleeve  173  may be made entirely of low coercivity ferromagnetic material. Together with pole pieces  131 A and  131 B, they may form a magnetic circuit  220 E, which is shown in  FIGS. 1B . A magnetic circuit is a structure operative to be the pathway for an operative portion of the magnetic flux from a magnetic flux source. Magnetic circuit  220 E provides a pathway for magnetic flux that is generated by electromagnet  119  and is operative to actuate latch pin  114 A from its engaging to its non-engaging position. When electromagnet  119  is first energized, magnetic circuit  220 E includes the air gap  134 A, which is shown in  FIG. 1A . Energizing electromagnet  119  generates magnetic flux that polarizes low coercivity ferromagnetic materials within circuit  220 E and results in magnetic forces on latch pin  114 A that tend to drive it to the non-engaging position shown in  FIG. 1B . Driving latch pin  114 A to the non-engaging configuration reduces air gap  134 A and the magnetic reluctance in circuit  220 E. If electromagnet  119  is switched off, spring  141  may drive latch pin  114 A back into the engaging configuration and reopen air gap  134 A. 
         [0087]    Magnetic circuit  220 E passes through rocker arm  103 A. In this disclosure, “passing through” a part means passing through the smallest convex volume that can enclose the part. When asserting that a magnetic flux that is operative “passes through” a part, the meaning is that the entirety of a portion of the magnetic flux that is sufficient to be operative passes through that part. In other words, the operability is achieved independently from any flux that follows a circuit that does not pass through the part. 
         [0088]    Magnetic circuit  220 E passes through the structure of rocker arm  103 A. “Passing through the structure” of a part means passing through the material that makes up that part. If the part forms a low reluctance pathway for the magnetic flux, it may help define the magnetic circuit. Low coercivity ferromagnetic materials in particular are useful in establishing magnetic circuits. In some cases, the magnetic properties of a part are essential to the formation of a magnetic circuit through which actuator  127  is operative. A touchstone for these cases is that if that part were replaced by an aluminum part, an operability dependent on that circuit would be lost. Aluminum is an example of a paramagnetic material. For the purposes of this disclosure, a paramagnetic material is one that does not interact strongly with magnetic fields. 
         [0089]    HLA  181  and latch pin  114 A form an essential part of magnetic circuit  220 E. In other words, if either of these parts were replaced by ones made entirely of aluminum, actuator  127  would cease to be operative to actuate latch pin  114 A. Depending on the strength of electromagnet  109 , the core structure of rocker arm  103 A may also form an essential part of magnetic circuit  220 E. Rocker arm  103 A may be formed of low coercivity ferromagnetic material that provides a low reluctance pathway for magnetic flux crossing from HLA  181  to latch pin  114 A. On the other hand, HLA  181  brings magnetic flux sufficiently close to latch pin  114 A that magnetic flux may cross between HLA  181  and latch pin  114 A following magnetic circuit  220 E regardless of the material in between. In some of these teachings, pole pieces  192 L are positioned to the sides of rocker arm  103 A as illustrated in  FIG. 22  to facilitate transmission of magnetic flux from HLA  181  to latch pin  114 A within rocker arm  103 A. 
         [0090]    Latch pin  114 A, by virtue of being mounted to outer arm  103 A, has a range of motion relative to combustion chamber  137  and actuator  127 A. This range of motion may be primarily the result of outer arm  103 A pivoting on HLA  181  when rocker arm assembly  115 A is in the engaging configuration. On the other hand, the position of latch  117 A relative to actuator  127 A may be substantially fixed while latch  117 A is in the non-engaging configuration. Extension and retraction of HLA  181  may introduce some relative motion but, excluding a brief period during start-up, the range of motion introduced by HLA  181  may be negligible. As long as latch pin  114 A is in the non-engaging configuration, magnetic circuit  220 E may remain operative whereby electromagnet  119  may act through that circuit to maintain latch pin  114 A in the non-engaging configuration. 
         [0091]      FIGS. 2A and 2B  are perspective views of a portion of the valvetrain  101 A, which is in accordance with some aspects of the present teachings and is a part of engine  100 A. As shown by these illustrations, actuator  127 A may be one of four supported by a common mounting frame  123 . The four actuators  127 A may control two intake ports and two exhausts ports for one engine cylinder. Mounting frame  123  may include four pole pieces  131 A joined with a paramagnetic connecting structure  122 . 
         [0092]    As shown in  FIGS. 3A-3C , mounting frame  123  may join with an upper frame  125  to support and protect a wiring harness  124 . Wiring harness  124  includes wires  128  that provide power to electromagnets  119 . Mounting frame  123  supports wiring harness  124  from below. Upper frame  125  may protect wires  128  from objects falling from above during manufacturing or maintenance. Upper frame  125  may include four pole pieces  131 B and a paramagnetic connecting structure  129 . 
         [0093]    Wires  128  may all connect to a common plug  126 . In some of these teachings, two of the electromagnets  119  are connected in series or in parallel. In some of these teachings, all four of the electromagnets  119  are connected in series or in parallel. These options reduce the number of wires in plug  126  and allowing a tradeoff between circuit costs and flexibility. For example, the intake and exhaust valves in a multi-valve engine may only be subject to deactivation in pairs. 
         [0094]    In accordance with some of the present teachings, mounting frame  123  is supported to two or more HLAs  181  that are angled with respect to one another when installed in their bores  174 . This angling may restrict vertical movement of mounting frame  123 . Mounting frame  123  may not fit over HLAs  181 . In an installation method, two or more HLAs  181  may be slid through openings in mounting frame  123  into their bores  174 . Electromagnets  119  and wiring harness  124  may be installed on mounting frame  123  either before or after this operation. Upper frame  125  may be connected to mounting frame  123  any time after the installation of electromagnets  119 . Mounting frame  123  may be further secured with connectors attaching frame  123  to cylinder head  130 . 
         [0095]    Mounting frame  123  may be part of a valve actuation module. In the present disclosure, a valve actuation module is a structure that includes a rocker arm assembly  115  and an actuator  127  according to the present disclosure. The actuator  127  may be mounted to a pivot for the rocker arm assembly  115 . For example, the actuator  127  may be mounted to an HLA  181 . In some of these teachings, the HLA  181  and the rocker arm assembly  115  are held together by a removable clip (not shown). The clip may hold HLA  181  and rocker arm assembly  115  together during shipping and through installation of valve actuation module within an engine  100 . 
         [0096]      FIG. 4  provides a perspective view of a portion of a valvetrain  101 B according to some other aspects of the present teachings. Valvetrain  101 B may be used in place of valvetrain  101 A in engine  100 A.  FIG. 5  provides a cross-sectional view of what valvetrain  101 B would look like in engine  100 A. Valvetrain  101 B may be the same as valvetrain  101 A except that valvetrain  101 B uses one or more latch assemblies  105 B in place of one or more latch assemblies  105 A. Latch assembly  105 B includes actuator  127 B and two latch pins  114 B. 
         [0097]      FIG. 6  illustrates the parts of actuator  127 B separately from other components of valvetrain  101 B. Actuator  127 B includes pole piece  131 C, pole piece  131 D, and electromagnet  119 . Pole piece  131 C may provide a core for electromagnet  119  and may be mounted to a pair of HLAs  181 . Pole piece  131 D may be mounted separately from pole piece  131 C. As shown in  FIGS. 4 and 5 , pole piece  131 D may be positioned between latch pins  114 B and an outer portion of engine  101 A, such as cylinder head  130 . Pole piece  131 D forms a low reluctance pathway for magnetic flux between two latch pins  114 B. Pole piece  131 D may be mounted to cylinder head  130 . 
         [0098]    Actuator  1278  places electromagnet  119  between two adjacent rocker arm assemblies  115 A. When electromagnet  119  is energized, it actuates the two latch pins  1148  to their non-engaging position through magnetic flux that follows the magnetic circuit  220 F illustrated in  FIG. 7 . Magnetic circuit  220 F includes pole pieces  131 C and  131 D, two HLAs  181 , two outer arms  103 A, and two latch pins  114 B. Magnetic flux from electromagnet  119  following magnetic circuit  220 F proceeds from electromagnet  119  through pole piece  131 C to one of the HLAs  181 , up the HLA  181 , through the associated rocker arm  103 A, through the latch pin  1148  mounted to that rocker arm  103 A, across an air gap  1348  to pole piece  131 D, through pole piece  131 D, across another air gap  1348  to the other latch pin  1148 , through the other rocker arm  103 A, down through the other HLA  181 , back into the pole piece  131 C, and from there back to electromagnet  119 . The magnetic flux polarizes low coercivity ferromagnetic materials throughout the circuit  220 F and place magnetic force on latch pins  1148  that causes them to actuate to the non-engaging position, narrowing the air gaps  1348  in the process. 
         [0099]    Referring to  FIG. 5 , latch pin  114 B is held within a hydraulic chamber  177  that is formed in rocker arm  103 A by a latch pin cage  110 . In accordance with some of these teachings, latch pin cage  110  is paramagnetic, which may improve the operation of latch assembly  1058 . In accordance with some of these teachings, latch pin  114 B has an expanded end  111  that does not fit within the opening in rocker arm  103 A out of which latch pin  114 B extends. Expanded end  111  may have a larger cross-sectional area than the core  113 B of latch pin  114 B that travels within hydraulic chamber  177 . End  111  may be relatively flat to fit closely against rocker arm  103 A. The large cross-sectional area of end  111  facilitates its interaction with pole piece  131 D. In accordance with some of these teachings, pole piece  131 D is mounted to be facing end  111  when cam  167  is on base circle. The facing surfaces are parallel or nearly parallel. In some of these teachings, the facing surfaces are generally flat. In some of these teachings, one or both of the facing surfaces has one or more dimples. In some of these teachings, latch pin  114  contacts an actuator pole piece  131  when latch pin  114  is in the non-engaging position. Dimples may be operative to prevent end  111  and pole piece  131 D from contacting over a large surface area and potentially sticking together. In some of these teachings the facing surfaces are parallel or nearly parallel to a direction of lash adjustment provided by lash adjuster  181 . This geometry may facilitate maintaining operability of actuator  127 B over a range of lash adjustment. 
         [0100]      FIG. 8  provides a flow chart of a method  300  by which engine  100 A may be operated. Method  300  begins with act  301 , rotating camshaft  169 . Rotating camshaft  169  may be inherent in running engine  100 A. Act  303  checks whether cam  167  is on base circle. Act  303  may be used to ensure that latch pin  114 A is actuated only when cam  167  is on base circle. Rather than simply limit the start of actuation to times when cam  303  is on base circle, act  303  may more narrowly limit the range of cam phase angles at which latch pin actuation may be initiated to ensure that actuation is complete before cam  167  begins to rise off base circle. Act  305  determines whether an unlatch command, such as a command to deactivate valve  185 , is currently in force. If yes, method  300  proceeds with act  307 , powering electromagnet  119  to actuate latch pin  114  if latch pin  114  is not already in the non-engaging position. If no and latch pin  114  is not already in the engaging position, method  300  proceeds with act  309  to deactivate electromagnet  119  thereby allowing latch pin  114  to actuate to the engaging position under the influence of spring  141  or the like. 
         [0101]    In some aspects of the present teachings, act  307  generates magnetic flux that enters a rocker arm  103  and actuates a latch pin  114  mounted on that rocker arm. Magnetic flux follows closed loops, so the flux that enters the rocker arm  103  also leaves the rocker arm  103  before returning to its source. In accordance with the present teachings, the flux that enters and leaves the rocker arm  103  is sufficient to result in latch pin  114  actuating. The source of magnetic flux may be relatively stationary with respect to combustion chamber  137 . Rocker arm  103 , on the other hand, is mobile with respect to combustion chamber  137 . In some of these teachings, act  307  places a magnetic force directly on the latch pin  114 . This force may initially actuate the latch pin  114  and subsequently maintain the position of latch pin  114  while the engine  100  continues to operate through act  301 . 
         [0102]    Act  307  may power electromagnet  119  with either an alternating current (AC) or a direct current (DC). In some of these teachings, act  307  powers electromagnet  119  with a DC current. In some of these teachings deactivating electromagnet  119  cuts power to electromagnet  119  entirely. But in some of these teachings, deactivating electromagnet  119  simply reduces the current or changes it in such a way that latch pin  114  ceases to be held in the non-engaging position. 
         [0103]      FIG. 9  provides a flow chart of an example method  310  according to some aspects of the present teachings. Method  310  may be used with valvetrain  101 A, valvetrain  101 B, or any other valvetrain in which a latch pin  114 A mounted to a rocker arm  103 A is actuated using an electromagnet  119  operating through a magnetic circuit  220  having an air gap  134  that varies in width in relation to a motion of rocker arm  103 A that actuates a poppet valve  185 . Method  310  may be carried out simultaneously with method  300  and includes the act  301  which has camshaft  169  in a state of rotation. Act  311  is determining whether electromagnet  119  is currently actively engaged in actuated latch pin  114  or maintaining latch pin  114 &#39;s position. The state of being active may be assumed if an unlatch state has been commanded. If not, method  310  proceeds with act  313 , which is a data collection step. 
         [0104]    Data collection may include measuring a current or voltage in an electrical circuit comprising electromagnet  119 . A time variation in that current or voltage may be measured. In method  310 , the electrical circuit is pulsed in connection with this data collection operation. That pulse may be insufficient in magnitude or duration to potentially actuate latch pin  114 . The data may be obtained using any suitable measuring device. Examples of measuring devices that may be suitable include, without limitation, a shunt resistor and a Hall effect sensor. 
         [0105]    Act  315  is determining the position of rocker arm  103 A from the collected data. The data will depend on the inductance of the circuit, which will depend on the inductance of electromagnet  119 , which will depend on the magnetic reluctance of a magnetic circuit  220 , which will depend on the size of air gap  134 , which will depend on the pivot angle of rocker arm  103 A on the fulcrum provided by HLA  181 , which determines the amount by which valve  185  has been lifted of its seat  186 . Analyzing the data may include one or more of comparing the data to results obtained during calibration, comparing the data to model predictions, comparing the data to data obtained during a previous cam cycle, comparing the data to data obtained at other cam phases, and comparing similar data obtained from other rocker arms. 
         [0106]    Act  317  is performing an operation that depends on the results of that analysis. In some of these teachings, that operation is an engine management operation. An engine management operation is one that affects a running state of engine  100 . For example, the rocker arm position information may be use in a control algorithm. In some of these teachings, the information also relates to camshaft position. The camshaft position may be determined with greater accuracy or reliability by combining the data with similar data obtained from a second circuit containing a second electromagnet that is operable to actuate a latch pin on another rocker arm assembly of the engine  100 . The camshaft position information may be used in the same way as information from a conventional camshaft position sensor. In particular, the information may be used to determine the timing of an ignition or a fueling event. 
         [0107]    In some of these teachings, the operation of act  317  is a diagnostic. A diagnostic operation may include a reporting step. The report may be made selectively. The report may be sending a signal, such as illuminating a warning light. In some of these teachings, the diagnostic operation includes recording a diagnostic code in a data storage device. The diagnostic code may later be read by a technician. 
         [0108]    In the example of method  310 , the voltage pulse is limited by act  311  to periods in which electromagnet  119  is not being energized to hold or actuate latch pin  114 . But the method does not need to be limited in that way. A pulse in voltage may be applied on top of a fixed voltage, whereby rocker arm position data may be obtained while electromagnet  119  is active to control a latch pin position. The size of air gap  134  is also affected by the position of latch pin  114 . Therefore, method  310  may be extended to determine whether latch pin  114  is in the extended or retracted position. 
         [0109]    In some of these teachings, information obtained from the circuit comprising electromagnet  119  is used to distinguish among three states. In the first state, latch pin  114  is in the non-engaging configuration. In the second state, latch pin  114  is in the engaging configuration and cam  167  is on base circle. In the third state, latch pin  114  is in the engaging configuration and cam  167  is off base circle. 
         [0110]    Method  310  collects data in conjunction with a voltage pulse. In another method provided by the present disclosure, the circuit including electromagnet  119  is driven continuously over extended periods in a way that enables the data collection but does not affect the position of latch pin  114 . The periods may be in excess of the time taken for camshaft  169  to complete a rotation. The drive current may be limited to prevent any effect on latch pin  114 . For example, the circuit may be driven with a low voltage to facilitate data collection without actuating latch pin  114 . In some of these teachings, an AC current is provided for data collection while a DC current is provided to influence the position of latch pin  114 . 
         [0111]    In another alternative provided by the present disclosure, the electrical circuit including electromagnet  119  is monitored passively. If there is magnetic flux in a circuit  220  comprising electromagnet  119 , any expansion or contraction of air gap  134  will produce a change in that flux and induce a current in electromagnet  119 . That induced current may be detected and analyzed to determine the change in air gap  134 . In some of these teaching, a permanent magnet is configured to continuously maintain a magnetic flux in circuit  220 . That flux may be insufficient to hold latch pin  114  in any particular position. 
         [0112]    In some of these teachings, method  310  or one of the variations thereof described above is used to detect a critical shift in rocker arm assembly  115 A. A critical shift is the case where latch pin  114  comes out of the engaging position while cam  167  is lifting rocker arm  1036 . If this happened, rocker arm  103 A will be driven by valve spring  183  to rapidly pivot from a lifted position like the one shown in  FIG. 1C  to its base circle position shown in  FIGS. 1D . In some of these teachings, a critical shift is detected from the speed with which inductance or a related property varies. In some of these teachings, a critical shift is detected from an induced current in the circuit. In some of these teachings, a critical shift is detected from data indicating a premature return to base circle. 
         [0113]      FIGS. 10A and 10B  provide cross-sectional views illustrating a latch assembly  105 C according to some other aspects of the present teachings. Latch assembly  105 C may be used in place of latch assembly  105 A in engine  100 A. Latch assembly  105 C include latch pin  114 C mounted on rocker arm  103 A and actuator  127 C, which is mounted to cylinder head  130 . Latch pin  114 C includes a low coercivity ferromagnetic core  113 C to which a latch pin head  111  is journaled. Actuator  127 C includes electromagnet  119  and pole pieces  131 C,  131 D, and  131 E. 
         [0114]      FIG. 10A  illustrates the non-engaging configuration and  FIG. 10B  illustrates the engaging configuration. The engaging configuration is maintained by spring  141 , which opens air gap  136 . The non-engaging configuration is obtained by energizing electromagnet  119 , which generates magnetic force on latch pin  114 C sufficient to overcome the force of spring  141  and close air gap  136  through magnetic flux travelling circuit  2201 . Magnetic circuit  2201  includes pole pieces  131 C,  131 D, and  131 E of actuator  127 C. Magnetic circuit  2201  also include core  113 C of latch pin  114 C and a pole piece  192 A fixed on rocker arm  103 A. A pole piece may be any part formed of low coercivity ferromagnetic material and located in a position where it is operative to complete a magnetic circuit. Because pole piece  192 A is fixedly attached to rocker arm  103 A, it may be considered part of rocker arm  103 A in the terminology of this specification and the claims that follow. 
         [0115]    Pole piece  192 A and pole piece  131 C form a sliding magnetic joint that keeps magnetic circuit  2201  closed even as rocker arm  103 A pivots through a range of motion on HLA  181 . The shapes of these pieces are illustrated by  FIGS. 11, 12 and 13 , which show cross-sections through actuator  127 C taken along lines  11 - 11 ,  12 - 12 , and  13 - 13  of  FIG. 10B .  FIGS. 11A, 12A, 13A  show the spatial relationships when rocker arm  103 A is not being lifted by any cam and  FIGS. 11B, 12B, 13B  show the relationships when rocker arm  103 A is lifted. As shown by these figures, pole piece  192 A and latch pin core  113 C may have cylindrical profiles. Pole pieces  131 E may be provided as two pieces curved to form half cylinders where they lie adjacent electromagnet  192  progressively flattening as they extend outward from electromagnet  119  and eventually forming planar shapes as shown in  FIGS. 11A and 11B  in the region where they are adjacent pole piece  192 A. In this region, pole pieces  131 E have surfaces extending along a direction in which pole piece  192 A moves relative to pole pieces  131 E as a result of rocker arm  103 A pivoting. That movement is essentially vertical. 
         [0116]    Maintaining the operability of magnetic circuit  2201  through a range of rocker arm  103 &#39;s motion has several potential applications. In some of these teachings, rocker arm  103 A is modified to include cam followers and valvetrain  101 A is modified with additional cams to provide an alternate valve lift profile, such as a low lift profile, for valve  185  when latch pin  103 B is in the non-engaging position. 
         [0117]      FIGS. 14A and 14B  provide cross-sectional views illustrating a latch assembly  105 D according to some other aspects of the present teachings. Latch assembly  105 D is another alternative to latch assembly  105 A that may be used in engine  100 A. Latch assembly  105 D includes latch pin  114 D, which may be mounted on rocker arm  103 A, and actuator  127 D, which may be mounted to cylinder head  130 . Latch pin  114 D includes a low coercivity ferromagnetic yoke  209  fixed around a paramagnetic core  113 C to which a latch pin head  111  is journaled. Actuator  127 D includes electromagnet  119  and pole pieces  131 D,  131 E, and  131 F.  FIG. 14A  illustrates latch pin  114 D in a non-engaging position and  FIG. 10B  illustrates latch pin  114 D in an engaging position. 
         [0118]    Latch assembly  105 D further includes parts that are fixedly mounted to rocker arm  103 A. These include permanent magnet  200 A, permanent magnet  200 B, and pole pieces  192 C,  192 D,  192 E, and  192 F. Permanent magnets  200 A and  200 B may be cylindrical. They are arranged with confronting polarity and separated by pole piece  192 D, which is also cylindrical. In accordance with some aspects of the present teachings, latch assembly  105 D provides latch pin  114 D with stability in either the engaging or the non-engaging position. The stability referred to here is a positional stability. A stable position may correspond to a local minimum in a potential energy that is variable over a bounded range. A position may be stabilized by restorative forces that are generated without external power. Restorative forces will tend to return latch pin  114 D to one of its stable positions if latch pin  114 D is displaced from that position by a small perturbation. Restorative forces may be provided by springs, permanent magnets, or a combination thereof. For example, latch assembly  105 A uses a spring  141  to stably maintain the engaging configuration. In latch assembly  105 D, restorative forces are provided by permanent magnets  200 A and  200 B. 
         [0119]    Permanent magnet  200 A stabilizes the position of latch pin  114 D in both the engaging and the non-engaging configurations. When latch pin  114 D is in the non-engaging configuration, absent magnetic fields from electromagnet  119  or any external source, magnetic circuit  220 A provides the path for an operative portion of magnetic flux from permanent magnet  200 A. The path for an operative portion of magnetic flux from a magnet is a path taken by the majority of flux from that magnet. Magnetic circuit  220 A passes from the north pole of permanent magnet  200 A, through pole piece  192 D, through yoke  209  of latch pin  114 D, through pole pieces  192 C, across to actuator  127 D and through pole pieces  131 F,  131 D, and  131 E of actuator  127 D, back to rocker arm  103 A through pole pieces  192 C, then through pole piece  192 F to the south pole of permanent magnet  200 A. 
         [0120]    Permanent magnet  200 B also stabilizes the position of latch pin  114 D in both the engaging and the non-engaging configurations. When latch pin  114 D is in the non-engaging configuration, magnetic circuit  220 C provides the path for an operative portion of magnetic flux from permanent magnet  200 B. Magnetic circuit  220 C passes from the north pole of permanent magnet  200 B, through pole piece  192 D, through yoke  209  of latch pin  114 D, through pole piece  192 B, to the south pole of permanent magnet  200 B. Magnetic circuit  220 C is shorter than magnetic circuit  220 A and does not pass through actuator  127 C. 
         [0121]    When latch pin  114 D is in the engaging position, absent magnetic fields from electromagnet  119  or any external source, magnetic circuit  220 B provides the path for an operative portion of magnetic flux from permanent magnet  200 A. Magnetic circuit  220 B passes from the north pole of permanent magnet  200 A, through pole piece  192 D, through yoke  209  of latch pin  114 D, through pole piece  192 F and  192 E, to the south pole of permanent magnet  200 A. Magnetic circuit  220 B is shorter than magnetic circuit  220 D and does not pass through actuator  127 C. 
         [0122]    In the engaging position, magnetic circuit  220 D provides the path for an operative portion of magnetic flux from permanent magnet  200 B. Magnetic circuit  220 D passes from the north pole of permanent magnet  200 B, through pole piece  192 D, through yoke  209  on latch pin  114 D, through pole pieces  192 F and  192 C, through pole pieces  131 E,  131 D, and  131 F of actuator  127 C, through pole piece  192 B to the south pole of permanent magnet  200 A. 
         [0123]    In actuator  127 D, electromagnet  119  may be operative both to actuate latch pin  114 D from the engaging position to the non-engaging position and from the non-engaging position to the engaging position. To enable this operability, circuitry (not shown) such as an H-bridge is provided that can be used to connect electromagnet  119  to a voltage source with either a forward polarity or a reverse polarity. If the current is started in a forward direction while latch pin  114 D is in the non-engaging position, the resulting magnetic field may reverse magnetic polarity in low coercivity ferromagnetic materials within magnetic circuit  220 A. This greatly increases the reluctance of magnetic circuit  220 A for flux from permanent magnet  200 A. Magnetic circuit  220 C is likewise affected. Magnetic flux from permanent magnets  200 A and  200 B may be shifted away from magnetic circuits  220 A and  220 C and toward magnetic circuits  220 B and  220 D. The resulting magnetic forces on latch pin  114 D may drive it toward the engaging position. Latch pin  114 D may reach the engaging position and tend to remain there even after electromagnet  119  has been disconnected from its power source. If the current is subsequently started in a reverse direction while latch pin  114 D is in the engaging positon, the entire process may be reversed and latch pin  114 D returned to the non-engaging position. 
         [0124]    Yoke  209  of latch pin  114 D may have a stepped edge. Pole pieces  192 E may be shaped to mate with that edge. During actuation, magnetic flux may cross an air gap between yoke  209  and pole pieces  192 E. The stepped edge may increase the magnetic forces through which latch pin  114 D is actuated between its engaging and non-engaging positions. 
         [0125]    Sliding magnetic joints may be used to keep magnetic circuits  220 A and  220 D operative to help maintain the position stability of latch pin  114 D throughout the range of motion of rocker arm  103 A. These sliding magnetic joints are illustrated by  FIGS. 15A, 16A, and 17A , which illustrate cross-sections through actuator  127 D taken along the lines  15 - 15 ,  16 - 16 , and  17 - 17  respectively of  FIG. 14B .  FIGS. 15B, 16B, and 17B  illustrate corresponding cross-sections, but with changes resulting for rocker arm  103 A being lifted by a cam. 
         [0126]    As illustrated by these figures, a first sliding magnetic joints is formed between pole pieces  192 C and  131 E and a second sliding magnetic joint is formed between pole pieces  192 B and  131 F. At any given time, one joint carries flux from rocker arm  103 A to actuator  127 D and the other returns flux from actuator  127 D to rocker arm  103 A. All these pole pieces form nearly planar surfaces in areas where they come adjacent each other. Pole piece  192 C and  192 B flatten as they extend toward actuator  127 D. Likewise, pole pieces  131 E and  131 F flatten toward planar and square shapes as they extend toward rocker arm  103 A. Providing each pole piece with a surface extending in the direction of motion allows the two surface to remain proximate and provide a large area for magnetic flux transfer throughout the range of motion. 
         [0127]    As the used in the present disclosure, a sliding joint in a magnetic circuit may refer to two parts in a magnetic circuit that are separated by an air gap and are configured to undergo relative motion without the air gap varying much in size. A variation that remains less than 50% may be considered not much for purposes of this definition. In some of these teachings, one of the parts forming the sliding joint has a surface adjacent the air gap that is substantially parallel to a direction along which one of the parts is free to move relative to the other. 
         [0128]      FIG. 18  is flow chart of a method  320  providing an example of how an engine  100  having a bi-stable latch assembly  105  may be operated in accordance with some aspects of the present teaching. Method  320  may include acts  301  and  303  of method  300 . Method  320  includes a decision step  321  that may be similar to the decision step  305  of method  300 . The decision step  321  determines whether an unlatched state of latch pin  114  has been commanded. If it has, action may be predicated on whether latch pin  114  is believed to be in the latched state. That belief may be based on a previous execution of a latching operation or on diagnostic feedback relating to the position of latch pin  114 . If that predicate is not satisfied, method  320  may continue with action  301 . In some of these teachings, however, that predicate is not implemented. Actuating a bi-stable latch pin  114  may require little power and a redundant attempt to actuate latch pin  114  to a position it is already in may be harmless. 
         [0129]    If an unlatch state is commanded, method  320  may continue with act  323 , powering electromagnet  119  with a current in a first direction. Energizing electromagnet  119  with a current in a first direction may include connecting a circuit (not shown) comprising electromagnet  119  to a DC voltage source (not shown). If an unlatched state is not commanded, that may be equivalent to a command for a latched state and method  320  may continue with act  325 , powering electromagnet  119  with a current in a reverse of the first direction. Energizing electromagnet  119  with a current in a reverse direction of the first direction may include coupling electromagnet  119  to the same voltage source, but with a reverse polarity. The reversal of polarity may be accomplished with an H-bridge. 
         [0130]    Following act  323  or  325 , method  320  optionally continues with act  327 , scheduling an interruption of the current being supplied to electromagnet  119 . Interrupting the power supply after it is no longer required saves energy. In some of these teachings, the time for interrupting the power is predetermined. Only a brief time is required for latch pin actuation. An entire actuation operation may be completed while cam  167  is on base circle. In a bi-stable latch, the power may be interrupted before actuation is entirely complete. The latch pin stabilizing forces may complete the motion. In some of these teachings, the time for interrupting the current is determined by monitoring the current in a circuit comprising electromagnet  119 . Under a constant voltage, the current in a circuit comprising electromagnet  119  will vary as latch pin  114  actuates. The current will become steady after latch pin actuation has completed. After power has been disconnected, engine  100  continues to operate through act  301  and the position of latch pin  114  is maintained by springs, permanent magnets, or a combination thereof. In some of these teaching, an operative portion of flux from a permanent magnet  200  that maintains latch pin  114  mounted on rocker arm  103  in a stable position follows a flux path that includes an actuator  127  that is not mounted on the rocker arm  103 . 
         [0131]      FIGS. 19A and 19B  provide cross-sectional views illustrating a latch assembly  105 E according to some other aspects of the present teachings. Latch assembly  105 E is another alternative to latch assembly  105 A that may be used in engine  100 A. Latch assembly  105 D includes actuator  127 E mounted off rocker arm  103 A and latch pin  114 C, which is mounted to rocker arm  103 A. Latch assembly  105 D is operative to stabilize the position of latch pin  114 C in both its engaging and non-engaging positions. Actuator  127 E includes electromagnet  119 , pole pieces  131 C,  131 G, and  131 E, and a permanent magnet  200 C. 
         [0132]    In latch assembly  105 E, when latch pin  114 C is in the non-engaging position, latch pin  114 C is held there by magnetic flux that is generated by permanent magnet  200 C and follows a magnetic circuit  220 G. Magnetic circuit  220 G provides the path for an operative portion of permanent magnet  200 C&#39;s magnetic flux. Magnetic circuit  220 G passes from the north pole of magnet  200 C through pole pieces  131 D and  131 E of actuator  127 E, through pole piece  192 A, through latch pin  114 C, through pole pieces  131 C and  131 G of actuator  127 D to the south pole of magnet  200 C. Magnetic circuit  220 G may be maintained throughout the range of motion of outer arm  103 A by sliding magnetic joints, although that is not necessary if outer arm  103 A remains stationary while latch pin  114 C is in the non-engaging position. 
         [0133]    If electromagnet  119  of actuator  127 E is energized with current in a suitable first direction while latch pin  114 C is in the non-engaging position, some magnetic polarities in magnetic circuit  220 G may be reversed. Flux from permanent magnet  200 C may be redirected to a magnetic circuit  220 H, which is illustrated in  FIG. 19A . Magnetic circuit  220 H passes from the north pole of magnet  200 C through pole pieces  131 D,  131 E and  131 G of actuator  127 D, to the south pole of magnet  200 C. Magnetic circuit  220 H does not pass through latch pin  114 C. Energizing electromagnet  119  with current in the first direction disrupts the magnetic attraction between latch pin  114 C and pole piece  131 C allowing spring  141  to drive latch pin  114 C to the engaging position and hold it there. 
         [0134]    When latch pin  114 C moves to the engaging configuration, it introduces an air gap  136  into magnetic circuit  220 G. Air gap  136  greatly increases the magnetic reluctance of magnetic circuit  220 G. Therefore, there may be little or no tendency for magnetic flux from permanent magnet  200 C to shift back to magnetic circuit  220 G until electromagnet  119  is energized with current in a reverse of the first direction. When electromagnet  119  of actuator  127 D is so energized, polarities in magnetic circuit  220 G may be re-established in a direction that attracts flux from permanent magnet  200 C. Permanent magnet  200 C and electromagnet  119  may then cooperate to magnetically actuate latch pin  114 C back to the non-engaging configuration where latch pin  114 C may be stably maintained by permanent magnet  200 C alone. 
         [0135]    Actuation in latch assemblies  105 D and  105 E occurs through a flux shifting mechanism. A flux-shifting mechanism involves redirecting the flux from a permanent magnetic from a first magnetic circuit to a second distinct magnetic circuit. In some of these teachings, the first and second circuits share a structural element formed of a low coercivity ferromagnetic material. A first magnetic polarity in that structural element favors the magnetic flux traveling the first circuit and a second polarity favors the magnetic flux traveling the second circuit. The availability of the second magnetic circuit may reduce the energy required to actuate a latch pin away from a position that is held by a permanent magnet with its flux following the first magnetic circuit. 
         [0136]      FIG. 20  illustrates and engine  100 F in accordance with some further aspects of the present teachings. Engine  100 F include a latch assembly  105 F and a switching rocker arm assembly  115 F. Switching rocker arm assembly  115 F include an inner arm  103 D and an outer arm  103 C. Latch assembly  105 F includes actuator  127 F mounted off rocker arm assembly  115 F and latch pin  114 D mounted to inner arm  103 D. Rocker arm  103 D includes a pole piece  192 K. Actuator  127 F includes a pole piece  131 J. These pole piece remain adjacent and close magnetic circuits formed by latch assembly  105 F throughout the ranges of motion of rocker arms  103 C and  103 D. 
         [0137]      FIGS. 21A-21C  illustrate the relative positioning of pole pieces  192 K and  131 J for various states of rocker arm assembly  115 F.  FIG. 21A  shows the relative positioning when neither rocker arm  103 C or  103 D is lifted by a cam.  FIG. 21B  shows the relative positioning when both rocker arm  103 C or  103 D are in positons of maximum lift with latch pin  114 D in a non-engaging configuration.  FIG. 21C  shows the relative positioning when both rocker arm  103 C or  103 D are in positons of maximum lift with latch pin  114 D in an engaging configuration. As can be seen from these illustrations, pole pieces  192 K and  131 J form a sliding magnetic joint and are able to keep magnetic circuits that include rocker arm  103 D, latch pin  114 D, and actuator  127 F closed throughout the ranges of motion of rocker arms  103 C and  103 D, in both engaging and non-engaging configurations, and without interfering with the rocker arm motions. Pole pieces  192 K and  131 J may remain continuously proximate over a large surface area. In some of these teachings, this same effect is achieved using pole pieces mounted to or incorporated within outer arm  103 C. That alternative structure may reduce the overall size of latch assembly  105 F. 
         [0138]    The rocker arms  103  of the examples herein are all rocker arms that have been put into production for use with a hydraulically actuated latch. For example, with reference to  FIG. 1A , latch pin  114 A is installed within a hydraulic chamber  177  of rocker arm  103 A. The surface  178  through which rocker arm  103 A contacts hydraulic lash adjuster  181  is shaped to form a hydraulic seal with lash adjuster  181 . In some of these teachings, rocker arm assembly  115  includes a hydraulic lash adjuster  181  that was put into production for use with a hydraulically latching rocker arm. Hydraulic lash adjuster  181  may include a port  179  configured to channel hydraulic fluid from cylinder head  130  to rocker arm  103 A. For hydraulic operation, a port for hydraulic fluid is formed by drilling a hole in rocker arm  103 A from surface  178  into hydraulic chamber  177 . That is a post-production step that need not be carried out when rocker arm  103 A is used for electromagnetic latching as described herein. 
         [0139]    The components and features of the present disclosure have been shown and/or described in terms of certain aspects and examples. While a particular component or feature, or a broad or narrow formulation of that component or feature, may have been described in relation to only one embodiment or one example, all components and features in either their broad or narrow formulations may be combined with other components or features to the extent such combinations would be recognized as logical by one of ordinary skill in the art.