Patent Description:
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. Valve operating systems are disclosed in <CIT>, <CIT> and <CIT>.

The complexity and demands for oil in some valvetrain systems can be reduced by replacing hydraulic latches with solenoid-actuated magnetic latches. According to some aspects of the present teachings, magnetic latches, like hydraulic latches, are incorporated into the rocker arm assembly. This may provide a compact design suitable for the limited space available under the valve cover, but conventionally powering rocker arm assembly-mounted solenoid-actuated magnetic latches could involve attaching wire pairs to the rocker arm assemblies. Rocker arm assemblies reciprocate rapidly over a prolonged period and in proximity to other moving parts. Wires attaching to the rocker arm assemblies could be caught, clipped, or fatigued and consequently short out.

The present teachings relate to a valvetrain for an internal combustion engine. as claimed in claim <NUM>. The internal combustion engine includes a cylinder head, a poppet valve having a seat formed within the cylinder head, a cam shaft, a cam mounted to the cam shaft, and a rocker arm assembly including a rocker arm, a cam follower, and a magnetic latch including a latch pin. An actuator for the magnetic latch includes a solenoid and is operative to cause the latch pin to translate between the first and second positions. Actuating the latch pin to the first position may configure the rocker arm assembly to actuate the poppet valve in response to rotation of the cam shaft to produce a first valve lift profile. Actuating the latch pin to the second position may configure the rocker arm assembly to actuate the poppet valve in response to rotation of the cam shaft to produce a second valve lift profile, which is distinct from the first valve lift profile, or may deactivate the poppet valve.

The magnetic latch is mounted to a rocker arm of the rocker arm assembly and the actuator is mounted off the rocker arm. In some of these teachings, the actuator is mounted in a position that is fixed with respect to the cylinder head of the internal combustion engine. In some of these teachings, the solenoid is mounted to the cylinder head, a cam carrier, or a valve cover. Mounting off the rocker arm allows the wire positions to be static.

The actuator is operative to cause the latch pin to actuate or maintain a latch pin position through a magnetic field that crosses an air gap between the actuator and the magnetic latch. In some of these teachings, the solenoid 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 the flux from the permanent magnet and thereby cause the latch pin to actuate.

In some of these teachings, a low coercivity ferromagnetic portion of the magnetic latch extends out from the rocker arm in the direction of the actuator to facilitate the interaction between the magnetic latch and the actuator. In some of these teachings, that portion of the magnetic latch is part of the latch pin. In some of these teachings, that portion of the magnetic latch is a pole piece that is rigidly mounted to the rocker arm.

According to some aspects of the present teachings, the magnetic latch has both engaging and non-engaging configurations that are stable independently from the actuator. The two configurations may correspond to the first and second positions of the latch pin. In some of these teachings, the internal combustion engine has circuitry operable to energize a solenoid of the actuator with a current in either a first direction or a reverse of the first direction. The solenoid powered with current in the first direction maybe operative to actuate the latch pin from the first position to the second position. The solenoid powered with current in the second direction may be operative to actuate the latch pin from the second position to the first position. In some others of these teachings, the electromagnetic latch assembly includes two solenoids, one for latching and the other for unlatching. The two solenoids may have windings in opposite directions.

According to some aspects of the present teachings, a permanent magnet is operative to stabilize the latch pin in both the first and the second positions. In some of these teachings, the permanent magnet is part of the magnetic latch. 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 solenoid or other external sources, when the latch pin is in the first position, the majority of magnetic flux from the permanent magnet follows a first magnetic circuit and when the latch pin is in the second position, the majority of 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'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. In some of these teachings, the element is part of the latch pin. A magnetic latch operating on a flux-shifting principle may be made compact and thus more suitable for mounting on a rocker arm.

According to some aspects of the present 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 solenoid. In some of these teachings, the other circuit does not pass through the actuator. The circuit not passing through the actuator may be much shorter, have lower magnetic flux leakage, and allow the permanent magnet to apply a greater holding force to the latch pin.

In some of these teachings, the magnetic latch 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 also be part of the magnetic latch or part of the actuator. When the latch pin is in the first position, the majority of magnetic flux from the second permanent magnet follows a third magnetic circuit and when the latch pin is in the second position, the majority of magnetic flux from the permanent magnet follows a fourth magnetic circuit distinct from the third magnetic circuit. The actuator may be operative to redirect the second permanent magnet'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 actuator and facilitate actuation of the latch pin though operation of the solenoid.

According to some aspects of the present teachings, a permanent magnet that is operative to stabilize the latch pin in both its first and second positions is mounted fixedly with respect to a rocker arm on which the magnetic latch is mounted. Fixing the permanent magnet to the rocker arm means not fixing the permanent magnet to the latch pin. Taking the weight of the permanent magnet off the latch pin may increase actuation speed and allow the use of a smaller solenoid. In some of these teachings, the permanent magnet is annular. In some of these teachings, the permanent magnet if polarized in the direction the latch pin translates. In some of these teachings, the permanent magnet is positioned concentrically with respect to the latch pin. A permanent magnet so configured may provide a compact design. In some of these teachings, there are two such permanent magnets arranged with confronting polarity. In some of these teachings, the two magnets are at opposite ends of the magnetic latch. In some of these teachings, an annular ring of low coercivity ferromagnetic material is located between the two magnets. The annular ring may provide a pole piece for both magnets.

According to some aspects of the present teachings, the magnetic latch is mounted to a rocker arm of the rocker arm assembly and, along with the rocker arm, has a range of motion relative to the actuator. The position of the magnetic latch relative to the actuator may be affected at times by the position of the cam. In some of these teachings, the rocker arm assembly and the magnetic latch are configured such that the actuator does not need to be operative on the latch except within a limited portion of latch's range of motion. In some of these teachings, the magnetic latch is operative to keep the latch pin position stable independently from the actuator in both the engaging and non-engaging configurations. Actuation may be effectuated only when the cam is on base circle.

In some of these teachings, the rocker arm assembly is configured whereby the rocker arm to which the magnetic latch is mounted remains substantially stationary when the latch pin is in a non-engaging configuration. The engaging configuration may be maintained by the magnetic latch 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 when the rocker arm is in one particular position, a structure maintaining sufficient proximity between the solenoid and the magnetic latch 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 apply a magnetic force to the latch pin sufficient to overcome the spring force and hold the latch pin in the non-engaging configuration.

In some aspects of these teachings, the actuator is operative on the magnetic latch throughout the magnetic latch's range of motion. In some of these teachings, that operability is a result of the magnetic latch and the actuator being configured such that their relative motion is limited to a relatively narrow range. In some of these teachings, the magnetic latch may be configured near a pivot point for the rocker arm to which the magnetic latch is mounted. In some of these teachings, the rocker arm pivots on a fulcrum, the poppet valve is to one side of the fulcrum, and the actuator is to the opposite side of the fulcrum. The fulcrum may be a hydraulic lash adjuster. In some of these teachings, one of the first and second latch pin positions is maintained by a spring. The actuator may be operative to generate a magnetic field of sufficient strength to overcome the spring force and maintain the other of the first and second latch pin positions as the magnetic latch travels through its range of motion.

According to some aspects of the present teachings, the operability of the actuator throughout the magnetic latch's range of motion is maintained by one or more sliding joints in a magnetic circuit through which the actuator affects the magnetic latch. The magnetic circuit may include the latch pin. In some of these teachings, the latch pin can move in conjunction with rocker arm motion without breaking the magnetic circuit. The actuator and the magnetic latch may include one or more pole pieces that form the sliding magnetic joint. One part of the sliding magnetic joint may be attached to the actuator while the other part of the sliding magnetic joint may be attached to the magnetic latch. In some of these teachings, the magnetic circuit is operative as a primary path for magnetic flux from the solenoid. In some of these teachings, the magnetic circuit is operative as a primary path for magnetic flux from a permanent magnet that stabilizes the latch pin in an engaging or non-engaging configuration. In some of these teachings, the sliding magnetic joint completes magnetic circuits through which one or more permanent magnets stabilize the latch pin in both its engaging and non-engaging configurations.

In some of these teachings, the magnetic latch has a first low coercivity ferromagnetic component that moves with the rocker arm, the actuator has a second low coercivity ferromagnetic component, and one of the first and second components has a surface extending along the direction in which the first component moves. 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 component have surfaces extending along the direction of relative motion. Providing both components 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.

In some of these teachings, the magnetic latch has a low coercivity ferromagnetic component an outer portion of which travels an arc as the rocker arm moves through its range of motion and the actuator has a low coercivity ferromagnetic component with a surface parallel to the arc and positioned to remain in proximity to the arc throughout the rocker arm's range of motion. The two components may form a sliding joint for a magnetic circuit.

In some of these teachings, a magnetic circuit that is operative as a primary path for magnetic flux from the solenoid or a permanent magnet includes an air gap spanning between the magnetic latch and the actuator. The latch and the actuator may be configured whereby the width of the air gap does not vary by more than <NUM>% over the first rocker arm range of motion. A magnetic circuit may include two air gaps spanning between the magnetic latch and the actuator. Magnetic flux traveling from the magnetic latch to the actuator may cross the first air gap and magnetic flux from the actuator to the magnetic latch may cross the second air gap. In some of these teachings, variation in the widths of both air gaps are limited during rocker arm motion by sliding magnetic joints.

According to some aspect of the present teachings, a magnetic latch mounted to a rocker arm includes a latch pin a portion of which is formed of a low coercivity ferromagnetic material and protrudes from the rocker arm in the direction of the actuator. Energizing the solenoid may be operative to actuate the latch pin in such a way that a variable air gap between the protruding portion of the latch pin and the actuator is reduced. In some of these teachings, pole pieces from the actuator extend proximate the latch pin, whereby magnetic flux from the solenoid follows a magnetic circuit that passes directly from the pole pieces to the latch pin before returning to the actuator across the variable air gap. In some alternate teachings, the pole pieces extend proximate pole pieces forming part of the magnetic latch; pole pieces of the magnetic latch extend proximate the latch pin; and the magnetic flux from the solenoid follows a magnetic circuit from the pole pieces of the actuator to the pole pieces of the magnetic latch and from there into the latch pin before returning to the actuator across the variable air gap.

According to some aspects of the present teachings, the magnetic latch 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's range of motion. Nevertheless, a magnetic circuit may be formed between the actuator and a latch pin of the magnetic latch. Moreover, in some of these teachings, a magnetic circuit may be maintained and stabilize the latch pin position throughout the second rocker arm'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 magnetic latch 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 a magnetic circuit that includes the magnetic latch and the actuator.

The effectiveness of the actuator depends on its positioning relative to the magnetic latch. The effect of variations in that positioning due to manufacturing tolerances may be ameliorated by one or more sliding magnetic joints. According to some aspects of the present teachings, the actuator comprises one or more members extending from the actuator to engage the sides of the rocker arm assembly. These members may facilitate the positioning of the actuator relative to the latch pin. In some of these teachings, the members engage the rocker arm assembly without attaching to the rocker arm assembly. In some of these teachings, the members engage a fulcrum of the rocker arm assembly.

Some 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 magnetic latch mounted to a rocker arm. The latch 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 magnetic latch in one of the engaging and non-engaging configurations. A solenoid of an actuator that is mounted off the rocker arm is energized to cause the magnetic latch to change its configuration. The engine is then further operated with the magnetic latch in the other of the engaging and non-engaging configurations. In some of these teachings, energizing the solenoid is limited to a predetermined portion of the cam cycle. The predetermined portion of the cam's cycle may correspond to the time that the cam is on base circle. In some of these teachings, the solenoid generates a magnetic field that crosses an air gap between the actuator and the latch to act on the latch.

Some of these teachings relate to the case in which the magnetic latch is stable in both engaging and non-engaging configuration. According to some aspects of the present teachings, a method of operating the engine includes operating the engine while using a permanent magnet to maintain a magnetic latch mounted to a rocker arm in an engaging configuration. A solenoid of an actuator that is mounted off the rocker arm is energized to redirect the magnetic flux from the magnet and cause the magnetic latch to switch to a non-engaging configuration. The engine is then further operated with the permanent magnet maintaining the magnetic latch in the non-engaging configuration. The solenoid may then be energized again, this time with a current in the reverse direction, to again redirect the magnetic flux from the magnet and cause the magnetic latch to switch back to the engaging configuration.

The teachings of the present disclosure have been described primarily in terms of a magnetic latch mounted to a rocker arm and an actuator mounted off the rocker arm. However, some of the present teachings are applicable to valvetrains in which the magnetic latch is mounted to another part of the rocker arm assembly and the actuator is mounted off that part. In some of these teachings, the magnetic latch is mounted to a part that is mobile relative to the cylinder head and the actuator is mounted to a part that is stationary relative to the cylinder head. In some of these teachings, the magnetic latch is mounted to a mobile portion of a hydraulic lash adjuster or to a lifter. The actuator may be mounted to the cylinder head itself.

The primary purpose of this summary has been to present certain of the inventors' 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' concepts or every combination of the inventors' 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 within the scope of the claims that follow.

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 <NUM>" is the same as "permanent magnet 200A, 200B, 200C".

<FIG> provides a partial-cutaway top view of a portion of an engine 100A in accordance with some aspects of the present teachings. The view of <FIG> includes a rocker arm assembly 115A and an actuator 127A. <FIG> illustrates a cross-section through the actuator 127A taken along the line <NUM>-<NUM> of <FIG>. <FIG> illustrates a cross-sectional side view of engine 100A taken along the line <NUM>-<NUM> of <FIG>. The view of <FIG> includes some parts of engine 100A in addition to those shown in <FIG>. Those additional parts include a poppet valve <NUM>, a cam shaft <NUM> on which is mounted a cam <NUM>, a hydraulic lash adjuster <NUM>, and more of the cylinder head <NUM>.

Rocker arm assembly 115A includes rocker arm 103A (an outer arm), rocker arm 103B (an inner arm), and a hydraulic lash adjuster (HLA) <NUM>. A cam follower <NUM> may be mounted to rocker arm 103B through bearings <NUM> and shaft <NUM>. Cam follower <NUM> is a roller follower. Alternatively, cam follower <NUM> may be a slider. A magnetic latch 117A is mounted to rocker arm 103A. Latch 117A includes a latch pin 114A, a spacer 139A, and a spring <NUM>. Latch pin 114A includes latch pin body 113A, latch head <NUM>. A portion <NUM> of latch pin 114A protrudes outward from rocker arm 103A in the direction of actuator <NUM>. The protruding portion <NUM> may be integral with latch pin body 113A. At least a part of portion <NUM> is formed of low coercivity ferromagnetic material.

Latch pin 114A is translatable between a first position and a second position. The first position may be a non-engaging position, which is illustrated in <FIG>. The second position may be an engaging position, which is illustrated in <FIG>. When latch pin 114A is in the engaging position, rocker arm assembly 115A may be described as being in an engaging configuration. When latch pin 114A is in the non-engaging position, rocker arm assembly 115A may be described as being in a non-engaging configuration.

Both rocker arms 103A and 103B may pivot on a shaft <NUM>. Openings <NUM> may be formed into the sides of rocker arm 103A to allow it to pivot on shaft <NUM> independently from rocker arm 103B without interference from shaft <NUM>, which is mounted to rocker arm 103B and extends outwardly to engage torsion spring <NUM>. Torsion spring <NUM> acts on shaft <NUM> to bias rocker arm 103B upward relative to rocker arm 103A and maintain engagement between cam follower <NUM> and cam <NUM>. Torsion spring <NUM> may be mounted to rocker arm 103A on trunnions <NUM>.

<FIG> shows the effect if cam <NUM> rises off of base circle with while latch pin 114A is in the engaging position. Latch head <NUM> may engage lip <NUM> of rocker arm 103B, after which rocker arm 103B and rocker arm 103A may be constrained to move in concert. HLA <NUM> may operate as a fulcrum on which rocker arm 103B and rocker arm 103A may pivot together, driving down on valve <NUM> via an elephant's foot <NUM>, compressing valve spring <NUM> against cylinder head <NUM>, and lifting valve <NUM> of its seat lifted of its seat <NUM> within cylinder head <NUM> with a valve lift profile determined by the shape of cam <NUM>. The valve lift profile is the shape of a plot showing the height by which valve <NUM> is lifted of its seat <NUM> as a function of angular position of cam shaft <NUM>.

<FIG> shows the effect if cam <NUM> rises off of base circle while latch pin 114A is in the non-engaging position. Cam <NUM> still drives rocker arm 103B downward. But in the non-engaging configuration, rocker arm 103A may remain stationary. Torsion springs <NUM> may yield before valve spring <NUM>, whereby rocker arm 103B merely pivots on shaft <NUM> without lifting valve <NUM> of its seat <NUM>. This configuration may provide deactivation of a cylinder with a port controlled by valve <NUM>. Alternatively, there may be additional cams that operate directly on rocker arm 103A independently from rocker arm 103B. These additional cams may provide a lower valve lift profile than cam <NUM>. Therefore, the non-engaging configuration for rocker arm assembly 115A may provide an alternate valve lift profile and rocker arm assembly 115A may provide a switching rocker arm.

Actuator 127A may be mounted to cylinder head <NUM>. Actuator 127A may be mounted using a bracket <NUM>, for example. Alternatively, actuator 127A could be mounted to another part on engine <NUM> that is stationary relative to cylinder head <NUM>. A cam carrier and a valve cover are examples of parts that engine <NUM> may include that would be stationary relative to cylinder head <NUM>. Actuator 127A is mounted off rocker arm assembly 115A. Alternatively, actuator 127A could be mounted to an outer sleeve <NUM> of HLA <NUM>. Outer sleeve <NUM> of HLA <NUM> may remain stationary relative to cylinder head <NUM>. Even if actuator 127A is mounted off rocker arm assembly 115A, it may still include alignment guides (not shown) that extend to engage the sides of HLA <NUM> or another part of rocker arm assembly 115A. Such guides may facilitate alignment of actuator 127A with latch 117A.

Actuator 127A may include a solenoid <NUM>, pole pieces 131A, 131B, 131C, and 131D, a spacer <NUM>, and a shell <NUM>. Pole pieces <NUM> may be formed of low coercivity ferromagnetic material. Pole piece 131A may provide be a core centrally located within solenoid <NUM>. Shell <NUM> may protect solenoid <NUM> from its surrounding environment and facilitate mounting of actuator 127A. Spacer <NUM> may facilitate proper spacing in magnetic circuits formed with pole pieces <NUM>. Accordingly, spacer <NUM> may be made of a steel that is not ferromagnetic.

A spring <NUM> may bias latch pin 114A toward and hold latch pin 114A in the engaging position. If solenoid <NUM> is energized while cam <NUM> is at or near base circle, the majority of magnetic flux from solenoid <NUM> may follow a magnetic circuit 220E illustrated in <FIG>. Magnetic circuit 220E includes pole pieces 131A-D, and low coercivity ferromagnetic portion <NUM> of latch pin 114A. Depending on the positon of latch pin 114A, magnetic circuit 220E may include an air gap <NUM> spanning between latch pin 114A and pole piece 131A. Air gap <NUM> may be reduced by translation of latch pin 114A toward the non-engaging position. Reducing the size of air gap <NUM> reduces the magnetic reluctance of magnetic circuit 220E. Accordingly, the magnetic forces will tend to reduce the size of air gap <NUM> and energizing solenoid <NUM> may be operative to overcome the force of spring <NUM>, translate latch pin 114A to its non-engaging position, and hold it there.

Latch 117A, by virtue of being mounted to rocker arm 103A, has a range of motion relative to cylinder head <NUM> and actuator 127A. This range of motion may be primarily the result of rocker arm 103A pivoting on HLA <NUM> when rocker arm assembly 115A is in the engaging configuration. But if latch 117A is in the non-engaging configuration, the position of latch 117A relative to actuator 127A may be substantially fixed. Extension and retraction of HLA <NUM> may introduce some relative motion. But excluding a brief period during start-up, the range of motion introduced by HLA <NUM> may be negligible. As long as latch pin 114A as in the non-engaging configuration, magnetic circuit 220E may remain intact whereby solenoid <NUM> may act through that circuit to maintain latch pin 114A in the non-engaging configuration.

In accordance with some aspects of the present teachings, pole piece 131D may be configured to be proximate latch pin protrusion <NUM> on multiple sides, including two opposite sides, when cam <NUM> is on base circle. Such a configuration is shown in <FIG> and may provide a large area through which magnetic flux may easily pass between latch pin 114A and pole pieces <NUM>. As shown in <FIG>, latch pin protrusion <NUM> may rise relative to actuator 127A as cam <NUM> lifts off base circle with rocker arm assembly 115A in the engaging configuration. In some of these teachings, pole piece 131D has a slot <NUM> to accommodate this upward motion. In some examples, HLA <NUM> may descend and cause latch pin protrusion <NUM> to drop substantially when engine 100A is shut down. In some of these teachings, another slot (not shown) may be formed in pole piece 131D to accommodate this motion as well.

<FIG> illustrate cross-sections of a portion of an engine 100B, which may be the same as the engine 100A except for the illustrated differences. Engine 100B provides another example in accordance with some aspects of the present teachings. Engine 100B includes rocker arm assembly 115B and actuator 127B. The view of <FIG> includes a portion of rocker arm assembly 115B and of actuator 127B. <FIG> illustrates rocker arm assembly 115B in a non-engaging configuration and <FIG> illustrates rocker arm assembly 115B in an engaging configuration.

Latch 117B includes latch pin 114B and pole piece 192A. Actuator 127B includes solenoid <NUM> and pole pieces 131A, 131B, and 131E. A pole piece, as the term is used in the present disclosure, may be any part formed with low coercivity ferromagnetic material. <FIG> illustrate cross-sections through the actuator 127B taken along the lines <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> of <FIG>, respectively. <FIG> illustrate corresponding cross-sections, but with changes resulting for cam <NUM> rising off base circle with rocker arm assembly 115B in the engaging configuration.

Pole piece 131A may be a core for solenoid <NUM>. Pole piece 131B may be a disc covering an end of solenoid <NUM> that is distal from latch 117B. There may be two pole pieces 131E. Each pole pieces 131E may have the form of a half cylinder where they lie adjacent solenoid <NUM>. Solenoid <NUM> may be cylindrical and the two pole pole pieces 131E may together form a cylindrical shell around solenoid <NUM>. Solenoid <NUM> may have any suitable shape. In some of the present teachings, pole pieces <NUM> fit closely around solenoid <NUM> to enhance its efficiency.

In accordance with some aspects of the present teachings, and as can be seen by comparing the cross-sections illustrated by <FIG>, pole pieces 131E of actuator 127B change their profile shape as they extend towards rocker arm assembly 115B. In some of these teachings, they flatten toward planar shapes. The planar shapes may be realized in the region where pole pieces 131E are adjacent pole piece 192A. As shown in <FIG>, the flattening of pole pieces 131E to a planar shape allows latch 117B including pole piece 192A to move with the rocker arm 103A without interfering with pole pieces 131E. While in this example, pole piece 192A remains cylindrical in cross-section as it extends adjacent pole pieces 131E, in some aspects of the present teachings, which are illustrated with other examples, pole piece 192A are split and flatten into planar shapes like pole pieces 131E. Such flattening may be used to provide a large areas through which magnetic flux may easily pass between pole pieces <NUM> of actuator <NUM> and pole pieces <NUM> of magnetic latch <NUM>.

In engine 100B, if solenoid <NUM> is energized it may generate magnetic flux that follows magnetic circuit 220F shown in <FIG>. Magnetic circuit 220F may include pole pieces 131A, 131B, and 131E of actuator 127B, pole piece 192A of latch 117B, latch pin 114B, and an air gap <NUM>. The operation of actuator 127B may be similar to that of actuator 127A. One difference is that the magnetic circuit 220F formed by actuator 127B and magnetic latch 115B transfers flux from the outer pole pieces 131E to latch pin 114B through pole pieces 192A. The structures of magnetic circuits 220E and 220F each have potential advantages in terms of efficiency and packaging.

<FIG> illustrates a cross-section of a portion of an engine 100C in accordance with some other aspects of the present teachings. Engine 100C includes rocker arm assembly 115C and an actuator 127C. Rocker arm 115C includes a rocker arm 103A to which is mounted a magnetic latch 117C having a latch pin 114C. Actuator 127C may remain in a fixed position with respect to cylinder head <NUM> while being operative on latch 117C throughout the range of motion of rocker arm 103A. Engine 100C includes circuitry (not shown) through which a voltage with either a forward polarity or a reverse polarity may be applied to solenoid <NUM> of actuator 127C. Actuator 127C is operative both to actuate latch pin 114C of latch 117C from either an engaging position, shown in <FIG>, to a non-engaging position, shown in <FIG>, and from the non-engaging position to the engaging position. <FIG> illustrate cross-sections through the actuator 127C taken along the lines <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> of <FIG>, respectively. <FIG> illustrate corresponding cross-sections, but with changes resulting for cam <NUM> rising off base circle with rocker arm assembly 115C in the engaging configuration.

Magnetic latch 117C includes a first permanent magnet 200A, a second permanent magnet 200B, and pole pieces 192C, 192D, 192E, and 192F. Latch pin 114C may include a latch pin body 113C to which a low coercivity ferromagnetic portion <NUM> of latch pin 114C is mounted. Actuator 127C includes solenoid <NUM> and pole pieces 131F, 131B, and 131E. As illustrated in <FIG>, magnetic latch 117C forms magnetic circuits 220A and 220D. Magnetic latch 117C and actuator 127C together form magnetic circuits 220B and 220C.

In accordance with some aspect of the present teachings, the pole pieces of actuator 127C and of latch 117C form nearly planar surfaces in areas where they approach each other to complete magnetic circuits. As illustrated by the cross-sections of <FIG>, pole piece 192C and 192B flatten toward a planar shape as they extend near pole pieces <NUM>. Likewise, pole pieces 131E flatten toward a planar shape as they extend toward where they lie adjacent pole pieces <NUM>. Pole piece131F may be cylindrical where it forms a core for solenoid <NUM>, but its surfaces flatten to form a rectangular cross-section as it extends to lie adjacent pole pieces 192B.

Actuator 127C may be operative to assist latch 117C in maintaining the position of latch pin 114C throughout the range of motion of rocker arm assembly 115C even if latch pin 114C is in the engaging position where relative motion between actuator 127C and latch 115C is highest. Even when solenoid <NUM> is not energized, actuator 127C may be operative on latch 115C by complete magnetic circuits <NUM> through which permanent magnets 200A and 200B stabilize the position of latch pin 114C.

In accordance with some aspects of the present teachings, latch pin 114C is stable in either the first position, which provides a non-engaging configuration for rocker arm assembly 115C shown in <FIG>, or in the second position, which provides an engaging configuration for rocker arm assembly 115C shown in <FIG>. The stability referred to here is a positional stability. A stable position may correspond to a local minima 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 114C to its stable position if latch pin 114C is displaced from that position by a small perturbation. Restorative forces may be provided by springs, permanent magnets, or a combination thereof. In engine 100C, restorative forces are provided by permanent magnets 200A and 200B.

Both permanent magnets 200A and 200B stabilize the position of latch pin 114C in both the engaging and the non-engaging configurations. When latch pin 114C is in the non-engaging configuration, absent magnetic fields from solenoid <NUM> or any external source, magnetic circuit 220A provides the primary path for magnetic flux from permanent magnet 200A. The primary path for magnetic flux from a magnet is a path taken by the majority of flux from that magnet. Magnetic circuit 220A passes from the north pole of permanent magnet 220A, through pole piece 192D, through low coercivity ferromagnetic portion <NUM> of latch pin 114C, through pole pieces 131A, 131B, and 131C of actuator 127C, through pole pieces 192B and 192C of magnetic latch 115C, to the south pole of permanent magnet 220A. Magnetic circuit 220C provides the primary path for magnetic flux from permanent magnet 200B. Magnetic circuit 220C passes from the north pole of permanent magnet 220B, through pole piece 192D, through low coercivity ferromagnetic portion <NUM> of latch pin 114C, through pole piece 192D, to the south pole of permanent magnet 220B. Magnetic circuit 220C is shorter than magnetic circuit 220A and does not pass through actuator 127C.

If solenoid <NUM> is energized with current in a forward direction while latch pin 114C is in the non-engaging configuration, the resulting magnetic field may reverse magnetic polarity in the low coercivity ferromagnetic materials throughout magnetic circuit 220A. This greatly increase the reluctance of magnetic circuit 220A for flux from permanent magnet 200A. Magnetic circuit 220C may also be affected. Magnetic flux from permanent magnets 200A and 200B may be shifted away from magnetic circuits 220A and 220C and the net magnetic forces on latch pin 114C may drive it toward the engaging configuration shown in <FIG>.

Latch pin 114C may reach the engaging configuration and remain there after solenoid <NUM> has been disconnected from its power source. When latch pin 114C is in the engaging configuration, absent magnetic fields from solenoid <NUM> or any external source, magnetic circuit 220D provides the primary path for magnetic flux from permanent magnet 200B. Magnetic circuit 220D passes from the north pole of permanent magnet 220B, through pole piece 192D, through low coercivity ferromagnetic portion <NUM> of latch pin 114C, through pole pieces 192B and 192C of magnetic latch 115C, through pole pieces 131A, 131B, and 131C of actuator 127C, through pole piece 192E to the south pole of permanent magnet 220A. In the engaging configuration, magnetic circuit 220B provides the primary path for magnetic flux from permanent magnet 200A. Magnetic circuit 220B passes from the north pole of permanent magnet 220A, through pole piece 192D, through low coercivity ferromagnetic portion <NUM> of latch pin 114C, through pole pieces 192F and <NUM>, to the south pole of permanent magnet 220A. Magnetic circuit 220B is shorter than magnetic circuit 220D and does not pass through actuator 127C.

In accordance with some aspects of the present teachings, permanent magnets 200A and 200B are fixedly mounted to rocker arm 103A and arranged with confronting polarity. A pole piece 192D is positioned between the confronting poles. Permanent magnets 200A and 200B and pole piece 192D may be annular in shape and mounted to be concentric with respect to latch pin 114C. While this provides a compact and efficient design, other shapes and configurations may be substituted.

Low coercivity ferromagnetic portion <NUM> of latch pin 114C may have a stepped edge. Pole pieces <NUM> of latch 115C may be shaped to mate with that edge. During actuation, magnetic flux may cross an air gap between latch pin 114C and pole pieces <NUM>. The stepped edge may increase the magnetic forces through which latch pin 114C is actuate from the second position to the first.

As illustrated in <FIG>, pole pieces 192C and 131E form a sliding magnetic joint. The distance between pole pieces 192C and 131E varies by less than <NUM>% as rocker arm 103A travels through its range of motion with latch pin 114C in the engaging position. As rocker arm 103A moves, pole piece 192C moves in a substantially vertical direction. Pole piece 192C has a surface extending in this direction of motion, whereby it may maintain its proximity to pole piece 131E throughout the range of motion. This surface is also parallel to an arc travelled by the outer surface of pole piece 192C. Parallel to an arc means parallel to a tangent of that arc.

As the used in the present disclosure, a sliding joint in a magnetic circuit may refer to an air gap between two parts in the circuit where the air gap does not change significantly in size as the two parts move relative to one another. A variation that remains less than <NUM>% is usually not significant. 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.

Pole pieces 192B and 131F form another sliding magnetic joint. The distance between pole pieces 192B and 131F varies by less than <NUM>% as rocker arm 103A travels through its range of motion with latch pin 114C in the engaging position. As rocker arm 103A moves, pole piece 192B moves in a substantially vertical direction. Pole piece 192B has a surface extending in this direction of motion, whereby it may maintain its proximity to pole piece 131F throughout the range of motion. Pole piece 131F also has a surface extending in this direction of motion, which could also be sufficient to maintain this proximity through the travel of pole piece 192B. 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. Since magnetic flux must complete a circuit, in some of the present teachings actuator <NUM> and latch <NUM> form at least two sliding magnetic joints.

<FIG> illustrates an engine 100D, which provides an example in which a permanent magnet 200C that is part of an actuator 127D mounted off rocker arm 103A is operative to stabilize the position of a latch pin 114D of a latch 117D that is mounted on rocker arm 103A. Latch pin 114D has both engaging and non-engaging positions in which its position is stable.

When latch pin 114D is in the non-engaging position, latch pin 114D is held there by permanent magnet 200C with magnetic circuit <NUM> providing the primary path for permanent magnet 200C's magnetic flux. Magnetic circuit <NUM> passes from the north pole of magnet 200C through pole pieces 131B, 131C of actuator 127D, through pole piece 192C of magnetic latch 115D, through latch pin 114D, through pole pieces 131A and 131F of actuator 137D to the south pole of magnet 200C. Magnetic circuit <NUM> may be maintained throughout the range of motion of rocker arm 103A by sliding magnetic joints, although in this example that is not necessary as rocker arm 103A remains stationary while latch pin 114D is in the non-engaging position.

If solenoid <NUM> is energized with current in a suitable first direction while latch pin 114D is in the non-engaging position, polarities in magnetic circuit <NUM> may be reversed. Flux from permanent magnet 200C may be redirected to a magnetic circuit <NUM>, which is illustrated in <FIG>. Magnetic circuit <NUM> passes from the north pole of magnet 200C through pole pieces 131B, 131C and 131F of actuator 127D, to the south pole of magnet 200C. Magnetic circuit <NUM> does not pass through latch pin 114D. Energizing solenoid <NUM> with current in the first direction disrupts the magnetic attraction between latch pin 114D and pole piece 192A allowing spring <NUM> to drive latch pin 114D to the engaging position and hold it there.

When latch pin 114D moves to the engaging configuration, it introduces an air gap <NUM> into magnetic circuit <NUM>. Air gap <NUM> greatly increases the magnetic reluctance of magnetic circuit <NUM>. Therefore, there may be little or no tendency for magnetic flux from permanent magnet 200C to shift back to magnetic circuit <NUM> until solenoid <NUM> is energized with current in a reverse of the first direction. When solenoid <NUM> is so energized, polarities in magnetic circuit <NUM> may be re-established in a direction that attracts flux from permanent magnet 200C. Permanent magnet 200C and solenoid <NUM> may then cooperate to magnetically actuate latch pin 114D back to the non-engaging configuration where latch pin 114D may be stably maintained by permanent magnet 200C alone.

Actuation in both latches 117C and 117D may occur 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.

Solenoid <NUM> may be considered an electromagnet. In the examples above, a solenoid <NUM> was positioned with a pole facing the rocker arm assembly <NUM>, including latch pin <NUM>. <FIG> illustrates an internal combustion engine 100E including a rocker arm assembly 106E and an actuator 127E. Engine 100E provides an example in which a solenoid <NUM> is positioned with its poles off axis from a latch pin 114E. This configuration may facilitate packaging of actuator 127E under a valve cover. <FIG> shows the non-engaging configuration. <FIG> shows the engaging configuration. <FIG> illustrates a cross-section of actuator 127E taken through line <NUM>-<NUM> of <FIG>. <FIG> illustrates cross-sections of latch 127E taken through lines <NUM>-<NUM> and <NUM>-<NUM> of <FIG>. <FIG> illustrates the cross-section taken through line <NUM>-<NUM> of <FIG>. <FIG> illustrates this cross-section after cam <NUM> has risen off base circle.

Both permanent magnets 200A and 200B may stabilize latch pin 114E in the engaging configuration. In the engaging configuration, most of the flux from permanent magnet 200A follows magnetic circuit <NUM> and most of the flux from permanent magnet 200B follows magnetic circuit <NUM>. Magnetic circuit <NUM> proceeds from the north pole of permanent magnet 200A, through pole piece 192J, through low coercivity ferromagnetic portion <NUM> of latch pin 114E, through pole pieces 192E and 192I, and ends at the south pole of permanent magnet 200A. Magnetic circuit <NUM> may be a short magnetic circuit contained entirely within magnetic latch 117E. Magnetic circuit <NUM> proceeds from the north pole of permanent magnet 200B, through pole piece 192D, through low coercivity ferromagnetic portion <NUM> of latch pin 114E, through a pole pieces 192E, <NUM>, and 192J of magnetic latch 117E, across a narrow air gap and onward through pole piece <NUM>, 131A, and <NUM> of actuator 127E, across another narrow air gap to pole piece <NUM> of magnetic latch 117E, and then through pole piece <NUM> to the south pole of permanent magnet 200B. Magnetic circuit <NUM> forms two sliding magnetic joints. Pole pieces <NUM> and <NUM> of actuator 127E may be planar in shape. Pole pieces <NUM> and 192J of magnetic latch 117E may be quarter cylinders. Pole piece <NUM> and <NUM> may be planar. Pole piece <NUM> may close off a space within magnetic latch 117E. Pole piece <NUM> may have an opening through which latch pin 114E translates.

Energizing solenoid <NUM> with a current in a suitable direction may redirect the flux from permanent magnets 200A and 200B and cause latch pin 114E to translate to a non-engaging position. As shown in <FIG> in the non-engaging configuration, after solenoid <NUM> has been disconnected from its power source, both permanent magnets 200A and 200B may again stabilize the position of latch pin 114E. In the non-engaging configuration, most of the flux from permanent magnet 200A follows magnetic circuit 220J and most of the flux from permanent magnet 200B follows magnetic circuit <NUM>. Magnetic circuit 220J proceeds from the north pole of permanent magnet 200A, through pole piece 192D, through low coercivity ferromagnetic portion <NUM> of latch pin 114E, through pole pieces <NUM> and 192Gof magnetic latch 117E, across a narrow air gap to131H and then through pole piece 131A and <NUM> of actuator 127E, across another narrow air gap to pole piece 192J of magnetic latch 117E, and then through pole piece <NUM> to the south pole of permanent magnet 200A. Magnetic circuit <NUM> proceeds from the north pole of permanent magnet 200B, through pole piece 192D, through low coercivity ferromagnetic portion <NUM> of latch pin 114E, through pole pieces 192E and <NUM> to the south pole of permanent magnet 200B. The process of actuating latch pin 114E to the non-engaging position may be reversed by applying a reversed polarity voltage to solenoid <NUM>.

<FIG> is flow chart of a method <NUM> providing an example in accordance with some aspects of the present teaching. Method <NUM> begins with act <NUM>, which is energizing a solenoid <NUM> to magnetically disengage a magnetic latch <NUM>. The solenoid <NUM> is mounted in a position that is stationary with respect to cylinder head <NUM>. In some of these teachings, that position is off rocker arm assembly <NUM>. In some of these teaching, that position is a portion of rocker arm assembly <NUM> that does not move relative to cylinder head <NUM>. The magnetic latch <NUM> may be on a mobile portion of a rocker arm assembly <NUM>. In some of these teachings, magnetic latch <NUM> is mounted to a rocker arm <NUM>. In some of these teachings, solenoid <NUM> generates a magnetic field that crosses from the actuator <NUM> to the latch to exert a magnetic force that actuates latch pin <NUM>. Energizing solenoid <NUM> may include coupling solenoid <NUM> to a voltage source.

In some of the present teachings, magnetic latch <NUM> is only actuated when cam <NUM> is on base circle. Any suitable method may be used to control the actuation timing. In some of these teachings, a signal to actuate magnetic latch <NUM> is only generated when cam <NUM> is on base circle. The signal may be generated by an engine control unit (not shown), for example. In some of these teachings, once a signal to actuate magnetic latch <NUM> is received, a controller delays engaging solenoid <NUM> with an energy source until cam <NUM> has arrived on base circle. In some of these teachings, solenoid <NUM> is energized before cam <NUM> reaches base circle to preload force on latch pin <NUM> and thereby accelerate actuation once the base circle position has arrived.

Method <NUM> continues with act <NUM>, using solenoid <NUM> to maintain the unlatched configuration while operating the rocker arm assembly <NUM>. Operating rocker arm assembly <NUM> may comprise rotating cam shaft <NUM>. Solenoid <NUM> may maintain the unlatched configuration by continuously generating a magnetic field that crosses from actuator <NUM> to latch <NUM> to exert a force that keeps latch <NUM> disengaged. In some of these teachings, the magnetic field from solenoid <NUM> maintains sufficient strength to overcomes a force from a spring <NUM> that continuously biases latch <NUM> toward the engaging configuration. In some of these teachings, a rocker arm <NUM> to which magnetic latch <NUM> is mounted moves but remains within solenoid <NUM>'s range during act <NUM>. In some of these teachings, a rocker arm <NUM> to which magnetic latch <NUM> is remains substantially stationary during act <NUM>.

The present disclosure provides several means by which solenoid <NUM> may maintain the latch configuration while the rocker arm assembly <NUM> is operating. In some of these teachings, rocker arm assembly <NUM> is configured to keep latch <NUM> substationally stationary while operating in the unlatched configuration. Rocker arm assemblies 115A-E can provide examples of such configurations. In some of these teachings, the motion of latch <NUM> relative to solenoid <NUM> may be sufficiently small that solenoid <NUM> remains operative on latch <NUM> through that motion. For example, the motion may be kept small by placing latch <NUM> near a pivot point for a rocker arm <NUM> on which latch <NUM> is mounted. Latches <NUM> of rocker arm assemblies 115A-E may be so configured. Continuous operability of solenoid <NUM> to maintain the position of latch <NUM> throughout the range of motion could be beneficial if the latches <NUM> are reconfigured so that spring <NUM> maintains the unlatched configuration and solenoid <NUM> maintains the latched configuration. In some of these teachings, a sliding magnetic joint is provided to make solenoid <NUM> operative to maintain the latch configuration throughout the range of motion of a rocker arm <NUM> to which latch <NUM> is mounted.

<FIG> is flow chart of a method <NUM> providing an example in accordance with some other aspects of the present teaching. Method <NUM> begins with act <NUM>, which is energizing solenoid <NUM> with a current in a first direction to magnetically disengage a magnetic latch <NUM>. As for method <NUM>, the solenoid <NUM> may be mounted in a position that is stationary with respect to cylinder head <NUM> while the latch <NUM> may be on a mobile portion of a rocker arm assembly <NUM>. In some of these teachings, solenoid <NUM> generates a magnetic field that crosses from actuator <NUM> to latch <NUM> to exert a force that disengages magnetic latch <NUM>. In some of these teachings, solenoid <NUM> redirects magnetic flux away from a circuit through which it maintains latch <NUM> in an engaging configuration. In some of these teachings, act <NUM> proceeds through a flux shifting mechanism.

Method <NUM> continues with act <NUM>, interrupting the current flow to solenoid <NUM> and maintaining the unlatched configuration of latch <NUM> while operating rocker arm assembly <NUM>. In these teaching, the unlatched configuration is maintained independently from solenoid <NUM>. In some of these teachings, latch pin <NUM> is stabilized in the unlatched configuration by permanent magnets <NUM>, latch springs <NUM>, or a combination thereof. In some of these teachings, even after solenoid <NUM> has been deenergized actuator <NUM> continues to be operative to assist maintaining latch pin <NUM> in the unlatched configuration by providing a portion of a magnetic circuit that is the primary circuit for magnet flux from a magnet <NUM> that assists in maintaining the unlatched configuration. In some of these teachings, the magnetic circuit is maintained through a sliding magnetic joint while rocker arm assembly <NUM> operates.

Method <NUM> continues with act <NUM>, which is energizing solenoid <NUM> with a current in a second direction, which is the reverse of the first direction, to magnetically engage magnetic latch <NUM>. In some of these teachings, solenoid <NUM> generates a magnetic field that crosses from actuator <NUM> to latch <NUM> to exert a force that engages latch <NUM>. In some of these teachings, solenoid <NUM> redirects magnetic flux away from a circuit through which it maintains latch <NUM> in a non-engaging configuration. In some of these teachings, act <NUM> proceeds through a flux shifting mechanism.

Energizing solenoid <NUM> with a current in a first direction may include connecting a circuit (not shown) comprising solenoid <NUM> to a DC voltage source (not shown). In some of these teachings, to energize solenoid <NUM> with a current in a reverse direction, the circuit is again connected to the voltage source, but with a reverse polarity. This may be accomplished with, for example, an H-bridge. Alternatively, different voltage sources may be connecting depending on whether a forward or reverse current is desired in solenoid <NUM>. In some others of these teachings, solenoid <NUM> may include a first set of coils to provide a magnetic field with a first polarity and a second, independently set of coils to provide a magnetic field with a second polarity. The two sets of coils may be electrically isolated and wound in different directions.

Method <NUM> continues with act <NUM>, interrupting the current flow to solenoid <NUM> and maintaining the latched configuration of latch <NUM> while operating rocker arm assembly <NUM>. In these teaching, the latched configuration is also maintained independently from solenoid <NUM>. In some of these teachings, latch pin <NUM> is stabilized in the latched configuration by permanent magnets <NUM>, latch springs <NUM>, or a combination thereof. In some of these teachings, even after solenoid <NUM> has been deenergized actuator <NUM> continues to be operative to assist maintaining latch pin <NUM> in the latched configuration by providing a portion of a magnetic circuit that is the primary circuit for magnet flux from a magnet <NUM> that assists in maintaining the latched configuration. In some of these teachings, the magnetic circuit is maintained through a sliding magnetic joint while rocker arm assembly <NUM> operates.

<FIG> illustrates and engine 100F in accordance with some further aspects of the present teachings. Engine 100F include an actuator 127F and a switching rocker arm assembly 115F. Switching rocker arm assembly 115F include an inner arm 103D, an outer arm 103C, and a magnetic latch 117F. Magnetic latch 117F and actuator 127F may be similar to magnetic latch 117D and actuator 127D except for the shapes of their pole pieces where they interface. Magnetic latch 117F includes a pole piece <NUM>. Actuator 127F includes a pole piece 131J. These pole piece remain adjacent and close magnetic circuits formed by magnetic latch 117F and actuator 127F through the ranges of motion rocker arms 103C and 103D.

<FIG> illustrate the relative positioning of pole pieces <NUM> and 131J for various states of rocker arm assembly 115F. <FIG> shows the relative positioning when neither rocker arm 103C or 103D is lifted by a cam. <FIG> shows the relative positioning when both rocker arm 103C or 103D are in positons of maximum lift with latch 117F in a non-engaging configuration. <FIG> shows the relative positioning when both rocker arm 103C or 103D are in positons of maximum lift with latch 117F in an engaging configuration. It can be seen from these illustrations that pole pieces <NUM> and 131J form a sliding magnetic joint and are able to keep magnetic circuits formed by magnetic latch 117F and actuator 127F closed throughout the ranges of motion of rocker arms 103C and 103D, in both engaging and non-engaging configurations, and without interfering with the rocker arm motions. Pole pieces <NUM> and 131J may remain continuously proximate over a large surface area. It may also be seen from these examples that similar circuits can be formed by mounting pole pieces to outer arm 103C.

Claim 1:
A valvetrain configured for an internal combustion engine (<NUM>) comprising a cylinder head (<NUM>), a poppet valve (<NUM>) having a seat (<NUM>) formed in the cylinder head (<NUM>), and a cam shaft (<NUM>) on which a cam (<NUM>) is mounted, comprising:
a rocker arm assembly (115A-115F) comprising a rocker arm (103A) and a cam follower (<NUM>) configured to abut the cam (<NUM>) mounted on the cam shaft (<NUM>)
a magnetic latch (<NUM>) comprising a latch pin (114A-114F) and a rocker arm-side pole piece (<NUM>) that are mounted on the rocker arm (<NUM>); and
an actuator (<NUM>) comprising an electromagnet (<NUM>) and an actuator-side pole piece (<NUM>) that are mounted off the rocker arm (103A);
wherein the latch pin (<NUM>) is moveable between a first position and a second position;
the rocker arm (<NUM>) is moveable independently from the actuator (<NUM>);
the electromagnet (<NUM>) is operable to cause the latch pin (<NUM>) to translate between the first position and the second position through magnetic flux that follows a magnetic circuit (<NUM>) that includes the rocker arm-side pole piece (<NUM>), the latch pin (<NUM>), the electromagnet (<NUM>), and the actuator-side pole piece (<NUM>); and
the actuator-side pole piece (<NUM>) extends proximate the rocker arm-side pole piece (<NUM>), whereby the magnetic flux that follows the magnetic circuit (<NUM>) passes between the actuator-side pole piece (<NUM>) and the rocker arm-side pole piece (<NUM>);
the rocker arm-side pole piece (<NUM>) extends proximate the latch pin (<NUM>) the magnetic flux that follows the magnetic circuit (<NUM>) passes from the rocker arm-side pole piece (<NUM>) to the latch pin (<NUM>);
the magnetic flux that follows the magnetic circuit (<NUM>) passes across a variable width air gap (<NUM>) between the actuator (<NUM>) and the latch pin (<NUM>).