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. In these systems, each rocker arm assembly 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.

The complexity and demands for oil in some valvetrain systems can be reduced by replacing hydraulic actuators with electromagnetic actuators. Accordingly, there has long been an interest in electromagnetically actuated latches for rocker arm assemblies. Electromagnetic actuators latches require power. 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. Attention is drawn to <CIT> , which relates to a valvetrain for an internal combustion engine of the type that has a combustion chamber, a moveable valve having a seat formed in the combustion chamber, and a camshaft. The valve train includes a rocker arm assembly, a pivot providing a fulcrum for a rocker arm of the rocker arm assembly, and a latch assembly. An electrical device mounted to the rocker arm assembly receives power or communicates through a circuit that includes an electrical connection formed by abutment between surfaces of two distinct parts. The rocker arm assembly is operative to move one of the two abutting surfaces relative to the other in response to actuation of the cam follower. Furthermore, <CIT> relates to an electromagnet which can attract a movable core against the force of a recovering spring and a current control circuit which supply an electromagnet coil a pulse current whose polarity is changed in accordance with the operation of a switch. In particular, a permanent magnet, which can attract a movable core against the expansion force of a recovering spring, is provided to a pole head of an electromagnet core. When a main contact is closed, an auxiliary contact is opened and a charging current is applied to an electromagnet coil to charge a capacitor and the flux, whose direction is the same as that of the permanent magnet, is induced in the electromagnet core and the movable core is attracted by the permanent magnet. The charging current is gradually reduced according to the charge of the capacitor but the movable core is kept to be attracted even after the charging current becomes null. When the closing contact is opened, the auxiliary contact is closed accordingly and the charge stored in the capacitor is discharged and the discharge current flows through the electromagnet coil, the auxiliary contact, a diode and a variable resistor and the original state is recovered. Another relevant document is <CIT>, which discloses a electromechanical latch assembly operated via a H-bridge circuit.

In accordance with the present invention, a valvetrain and a method as set forth in claims <NUM> and <NUM> are provided. Further embodiments are inter alia disclosed in the dependent claims. The present teachings relate to systems and methods for operating the valvetrain in an internal combustion engine of a type that has a combustion chamber, a moveable valve having a seat formed in the combustion chamber, a camshaft, and a rocker arm assembly that actuates the valve and includes and includes a rocker arm and a cam follower configured to engage a cam mounted on the camshaft as the camshaft rotates. The rocker arm assembly is configured such that rotation of the camshaft is operative to transmit force from the cam to the cam follower and move the rocker arm.

The rocker arm assembly includes a latch pin translatable between a first position and a second position. One of the first and second latch pin positions provides a configuration in which the rocker arm assembly is operative to actuate the moveable valve in response to actuation of the cam follower by the cam to produce a first valve lift profile. The other of the first and second latch pin positions provides a configuration in which the rocker arm assembly is operative to actuate the moveable valve in response to actuation by the cam follower by the cam to produce a second valve lift profile, which is distinct from the first valve lift profile, or the moveable valve is deactivated. This structure may provide cylinder deactivation (CDA) or variable valve lift (VVL).

The latch pin is part of an electromagnetic latch assembly that includes an electromagnet and in which the latch pin is stable independently from the electromagnet in both the first and the second positions. The latch pin is actuated from the first position to the second position by providing the electromagnet with a current in a first direction. The latch pin is actuated from the second position to the first position by providing the electromagnet with a current in a second direction, which is the reverse of the first. One or more permanent magnets may stabilize the latch pin in both the first and second positions.

In some of the present teachings, the electromagnet is mounted to a rocker arm of the rocker arm assembly. In some of these teachings, the electromagnet is powered through an electrical connection made by abutment between two distinct parts, one of which is mounted to the rocker arm. Movement of the rocker arm may cause relative motion between contacting surfaces of the abutting parts.

Conventionally, an H-bridge would be used to provide DC current that is selectively either in a first direction or a second direction. An H-bridge would require connections to both terminals of the electromagnet. But the present teachings recognize that it is possible to reduce the wire count and the number of couplings by grounding one terminal of the electromagnet and providing an actuator control system that connects to the other terminal to drive the electromagnet with a DC current that is selectively either in a forward or a reverse direction. In some of these teachings, one terminal of the electromagnet is grounded through the structure of the rocker arm assembly. In some of these teachings, the ground connection is made to a cylinder head of an engine.

Some aspects of the present teachings relate to an actuator control system suitable for providing single wire control of the electromagnets in a valvetrain system. The actuator control system includes a DC/DC converter and switching elements. In some of these teachings, the DC/DC converter is coupled to the electromagnets through one or more half-bridge circuits. A half-bridge circuit is less expensive than an H-bridge circuit.

In some of these teaching the actuator control system, when coupled to a DC power source, is operative to provide current in either a first direction or a second direction, which is a reverse of the first, to the first terminals of any selected one of a plurality of distinct groups comprising one or more of the electromagnets. The current in the first direction is provided by coupling the selected terminals directly to the power source. The current in the second direction is provided by the DC/DC converter. Accordingly, one DC/DC converter serves a plurality of electromagnet groups. This design relies on the latch pins associated with the various groups of electromagnets being actuated over brief and non-overlapping periods to reduce the number and size of components.

In accordance with some aspects of the present teachings, the DC/DC converter comprises one or more capacitors. The actuator control system provides current in a first direction to the first terminals in a group of the electromagnets by coupling those terminals to a DC power source. The DC power source is also used to charge the capacitors. The actuator control system draws down the capacitors to provide the first terminals of the electromagnets in the group with current in a second direction. Inverting DC/DC converters more commonly rely on inductors, where the energy for the reverse current is stored in the magnetic fields of the inductors. In the present design, energy for the reverse current is stored in the electric fields of the capacitors. The present teachings recognize that the timing of the valvetrain system allows for the use of a capacitor based DC/DC converter even when the actuator control system serves a plurality of groups of electromagnets. The capacitor based design reduces the number and complexity of parts.

Some aspects of the present teachings relate to a method of operating electromagnets in a valvetrain for an internal combustion engine of a type that has a combustion chamber, a moveable valve having a seat formed in the combustion chamber, and a camshaft. The electromagnets each have first and second terminals and each is operative to actuate a distinct group of one or more latch pins in rocker arm assemblies of the valvetrain. According to the method, over a first period the first terminals of a first set of the electromagnets are coupled to a DC power source to provide a current in a first direction to those terminals. Over a second period during which the DC power source is not coupled to the first terminals of the first set of the electromagnets, the DC power source is coupled to the first terminals of a second set of electromagnets, wherein the electromagnets in the second set are distinct from those in the first. The DC power source is also used to power a DC/DC converter. Over a third period, the DC/DC converter is coupled to the first terminals of the first set of the electromagnets and provides a current in a second direction to those terminals. The second direction is the reverse of the first. Over a fourth period during which the DC/DC converter is not coupled to the first terminals of the first set of the electromagnets, the DC/DC converter is coupled to the first terminals of the second set of the electromagnets. In some of these teachings, the DC/DC converter stores energy in one or more capacitors that drive the currents in the second direction.

Some aspects of the present teachings relate to another method of operating electromagnets in a valvetrain for an internal combustion engine of a type that has a combustion chamber, a moveable valve having a seat formed in the combustion chamber, and a camshaft. Each electromagnet is operative to actuate a distinct group of one or more latch pins. The method includes providing a first DC current from a power source to the first terminal of one of the electromagnets, wherein the first DC current actuates the latch pin from a first position to a second position; charging one or more capacitors with power from the power source; and providing a second DC current having an inverse polarity from the first DC current to the first terminal of the electromagnet. The second DC current is drawn from the one or more capacitors and the second DC current actuates the latch pin from the second position to the first position.

In some of these teachings, the actuator control system is installed in the engine along with the valvetrain. An engine control unit (ECU) may provide signals that that direct the actuator control system' provision of the currents in the forward and reverse directions. In some of these teachings, the DC/DC converter of the actuator control system exclusively serves the valvetrain system.

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 being reserved for the claims that follow.

<FIG> illustrate a valvetrain <NUM> with rocker arm assemblies <NUM>. Rocker arm assemblies <NUM> include outer arms 103A, inner arms 103B, and cam followers <NUM>. Valvetrain <NUM> is suitable for an internal combustion engine of a type that has combustion chambers, moveable valves having seats formed in the combustion chambers, and a camshaft. Rocker arm assemblies <NUM> may be installed in such an engine on pivots <NUM> in a configuration in which cams (not shown) on the camshaft engage cam followers <NUM> as the camshaft rotates. When rocker arms 103A and 103B are engaged, the action of the cams of the cam followers <NUM> is operative to actuate the moveable valves (not shown) via rocker arm assemblies <NUM>.

Rocker arm assemblies <NUM> may be cylinder deactivating rocker arms. With reference to <FIG>, cylinder deactivation is controlled by electromagnetic latch assemblies <NUM>, one of which is mounted to each rocker arm assembly <NUM>. Electromagnetic latch assemblies <NUM> each include a latch pin <NUM> that has extended and retracted positions. <FIG> shows latch pin <NUM> in the retracted position. When latch pin <NUM> is in the retracted position, rocker arms 103A and 103B are in a disengaged configuration. In the disengaged configuration, outer arm 103A may remain stationary even as inner arm 103B is driven to pivot through cam follower <NUM>. In this configuration, a valve actuated by rocker arm assembly <NUM> may be disabled. Latch pin <NUM> may be extended to place rocker arms 103A and 103B in an engaging configuration. In the engaging configuration, outer arm 103A may pivot in conjunction with inner arm 103B and a valve actuated by rocker arm assembly <NUM> may opened and closed in conjunction with actuation of rocker arm assembly <NUM> through cam follower <NUM>. Providing additional cams that operate directly on outer arm 103A can convert rocker arm assembly <NUM> into a two-step rocker arm providing two alternative valve lift profiles.

Electromagnetic latch assembly <NUM> includes permanent magnets <NUM> and <NUM>, and an electromagnet <NUM>, which is operative to actuate latch pin <NUM> between the extended and retracted positions. The operation of these components is illustrated by the sketches of <FIG> illustrates electromagnetic latch assembly <NUM> with latch pin <NUM> in the extended position, which is a first limit of travel for latch pin <NUM>. <FIG> illustrates electromagnetic latch assembly <NUM> with latch pin <NUM> in the retracted position, which is a second limit of travel for latch pin <NUM>. Electromagnet <NUM> is operative to cause latch pin <NUM> to translate between the extended and retracted positions. <FIG> illustrates the magnet field generated by electromagnet <NUM> to initiate the transition from the extended to the retracted position.

Permanent magnets <NUM> and <NUM> are each operative to stabilize the position of latch pin <NUM> in each of the extended and retracted positions. As illustrated in <FIG>, permanent magnets <NUM> and <NUM> utilize different magnetic circuits depending on whether latch pin <NUM> is in the extended or the retracted position. Pole pieces <NUM> and <NUM> form a clam shell around electromagnet <NUM>, which completes some of these magnetic circuits. Latch pin <NUM> has a magnetically susceptible ferrule <NUM> around a paramagnetic core <NUM>. Ferrule <NUM> is within these magnetic circuits and is the part through which permanent magnets <NUM> and <NUM> exert forces on latch pin <NUM>. Magnetic circuits have characteristics as described herein, but it should be appreciated that the illustrations of these magnetic circuits are only approximate.

For the purposes of this disclosure, a paramagnetic material is one that does not interact strongly with magnetic fields. Aluminum is an example of a paramagnetic material. A magnetically susceptible material is generally a low coercivity ferromagnetic material. Soft iron is an example of a low coercivity ferromagnetic material. Pole pieces <NUM>, <NUM>, and <NUM> and ferrule <NUM> may all be made from soft iron.

As shown in <FIG>, magnetic circuit <NUM> is the primary path for an operative portion of the magnet flux from magnet <NUM> when latch pin <NUM> is in the extended position, absent magnetic fields from electromagnet <NUM> or any external source that might alter the path taken by flux from magnet <NUM>. The operative portion of the flux is that portion of the magnetic flux which contributes to the stability of latch pin <NUM> in its current position. Magnetic circuit <NUM> proceeds from the north pole of magnet <NUM>, through pole piece <NUM>, through ferrule <NUM>, through an edge of pole piece <NUM>, and ends at the south pole of magnet <NUM>. Perturbation of latch pin <NUM> from the extended position would introduce an air gap into magnetic circuit <NUM>, increasing its magnetic reluctance. The magnetic forces produced by magnet <NUM> resist such perturbations.

As shown in <FIG>, when latch pin <NUM> is in the retracted position, magnetic circuit <NUM> is the primary path for an operative portion of the magnet flux from magnet <NUM>. Magnetic circuit <NUM> proceeds from the north pole of magnet <NUM>, through pole piece <NUM>, through ferrule <NUM>, through pole piece <NUM>, through pole pieces <NUM>, and ends at the south pole of magnet <NUM>. Perturbations of latch pin <NUM> from the retracted position would introduce an air gap into magnetic circuit <NUM>, increasing its magnetic reluctance. The magnetic forces produced by magnet <NUM> resist such perturbations.

Magnet <NUM> is also operative to stabilize latch pin <NUM> in both the extended and retracted positions. As shown in <FIG>, magnetic circuit <NUM> is the primary path for an operative portion of the magnet flux from magnet <NUM> when latch pin <NUM> is in the extended position and magnetic circuit <NUM> is the primary path for an operative portion of the magnet flux from magnet <NUM> when latch pin <NUM> is in the retracted position.

Electromagnetic latch assembly <NUM> is structured to operate through a magnetic flux shifting mechanism. In accordance with the flux shifting mechanism, electromagnet <NUM> is operable to alter the path taken by flux from permanent magnets <NUM> and <NUM>. <FIG> illustrates the mechanism for this action in the case of operating electromagnet <NUM> to induce latch pin <NUM> to actuate from the extended position to the retracted position. Current through electromagnet <NUM> results in magnetic flux that follows the circuit <NUM>. If the current has a suitable magnitude and direction, the flux reverses magnetic polarities in ferrule <NUM> and pole pieces <NUM> and <NUM>. This greatly increase the reluctance of magnetic circuits <NUM> and <NUM> causing flux following those circuits to shift toward magnetic circuits <NUM> and <NUM>. The net magnetic forces on latch pin <NUM> may drive it to the retracted position shown in <FIG>.

Referring to <FIG> and <FIG>, electromagnetic latch assembly <NUM>, which includes electromagnet <NUM>, may be installed in rocker arm 103A through opening <NUM> at the back of rocker arms 103A. Electromagnet <NUM> has a first terminal <NUM> and a second terminal <NUM>. In the illustrated example, wires <NUM> couple first terminal <NUM> to contact pad 104A and second terminal <NUM> to contact pad 104B.

While contact pad 104B may be used to form a ground connection, the present teachings provide for an alternative configuration in which second terminal <NUM> is grounded by a connection to rocker arm 103A or another load-bearing component of rocker arm assembly <NUM>. This alternative configuration eliminates the need for contact pad 104B and the electrical connection made through contact pad 104B.

Bracket <NUM>, which may be press fit into opening <NUM>, mounts contacts pads 104A and 104B to outer arm 103A and holds contacts pads 104A and 104B to one side of outer arm 103A over spring post <NUM>. Bracket <NUM> may also support wires <NUM>. Bracket <NUM> may include a part <NUM> held at the back of rocker arm 103A and a part <NUM> held to the side of rocker arm 103A. Optionally, parts <NUM> and <NUM> are provided as a single part. Such a part may be formed by over-molding wires <NUM> and contacts pads 104A and 104B.

Electromagnet <NUM> may be powered through electrical connections formed by abutment between spring-loaded pins 107A and 107B and contact pads 104A and 104B. Contact pads 104A and 104B are mounted to rocker arm 103A and move in conjunction with rocker arm 103A. Spring-loaded pins 107A and 107B are mounted to components distinct from rocker arm assembly <NUM>, whereby rocker arm 103A moves independently from spring-loaded pins 107A and 107B. Spring-loaded pins 107A and 107B are held against contact pads 104A and 104B respectively by framework <NUM>. As shown in <FIG>, framework <NUM> may include a base plate <NUM> and slip ring towers <NUM>. Base plate <NUM> may include cutouts <NUM> that fit around pivots <NUM>. When framework <NUM> is installed in an engine, baseplate <NUM> may rest atop a cylinder head (not shown) and abut two pivots <NUM>. Cutouts <NUM> may cooperate with pivots <NUM> to ensure proper positioning of framework <NUM> with respect to rocker arm assemblies <NUM> and therefore proper position of spring-loaded pins <NUM> with respect to contact pads <NUM>. Framework <NUM> may be secured to the cylinder head by bolts passing through openings <NUM>. This structure holds spring-loaded pins <NUM> stationary relative to the cylinder head even as contact pads <NUM> pivot in relation to the movement of rocker arm 103A.

With reference to <FIG>, contact pads 104A and 104B have planar contact surfaces 105A and 105B respectively. Each rocker arm assembly <NUM> pivots on a pivot <NUM>, which may be a hydraulic lash adjuster. Outer arm 103A and inner arm 103B are free to pivot relative to one-another except when they are engaged by latch pin <NUM>. Pivot <NUM> may raise or lower rocker arm assembly <NUM> to adjust lash. These motions take rocker arm 103A in directions parallel to the plane in which the planar contact surfaces contact pads 104A and 104B are oriented. Accordingly, the electrical connections formed by abutment between contacts pads <NUM> and spring-loaded pins <NUM> may be maintained as outer arm 103A goes through its range of motion.

Spring-loaded pin 107B may remain in abutment with contact surface 105B throughout rocker arm 103A's range of motion. Spring-loaded pin 107A may remain in abutment with contact surface 105A through only a portion of rocker arm 103A's range of motion. Contact pad 104A may be structured and positioned such that as rocker arm 103A is lifted off base circle, spring-loaded pin 107A moved from abutment with contact surface 105A to abutment with contact surface 105C. Connection through contact surface 105C may present a distinctly higher resistance than connection through contact surface 105A. The higher resistance may be provided by a coating on contact surface 105C that is not present on contact surface 105A. That coating may be a diamond-like carbon (DLC) coating. The difference in resistance may be used to detect the position of rocker arm 103A.

Any suitable structure may be used to mount contact pads <NUM> to rocker arm 103A. Likewise, spring-loaded pins <NUM> could be mounted to any suitable part that is distinct from rocker arm 103A. Spring-loaded pins <NUM> may be mounted to that distinct part by any suitable structure. Contact pads <NUM> may be the parts mounted to components distinct from rocker arm 103A while spring-loaded pins <NUM> may be mounted to rocker arm 103A. Pins <NUM> could be replaced by pins without springs. Contact pads <NUM> could be formed with leaf springs to bias pins <NUM> and contact pads <NUM> into abutment. Suitable contacts could also be formed with rollers or motor brushes. In general, there is at least one electrical connection formed by abutting surfaces one of which rolls or slides relative to the other in relation to rocker arm 103A being lifted by a cam. The present teachings are particularly useful when such a connection is present, but they extend to situations in which there is no such connection.

Electromagnet <NUM> is powered by circuitry that provides electromagnet <NUM> with DC current that is selectively either in a forward or a reverse direction. A conventional solenoid switch forms a magnetic circuit that include an air gap, a spring that tends to enlarge the air gap, and an armature moveable to reduce the air gap. Moving the armature to reduce the air gap reduces the magnetic reluctance of that circuit. Consequently, energizing a conventional solenoid switch causes the armature to move in the direction that reduces the air gap regardless of the direction of the current through the solenoid's coil or the polarity of the resulting magnetic field. As described above, however, the direction in which latch pin <NUM> is actuated depends on the polarity of the magnetic field generated by electromagnet <NUM>, which in turn depends on the direction of current through electromagnet <NUM>.

In the illustrated embodiment, two electrical connections are made to rocker arm 103A. To actuate latch pin <NUM> to the extended position, first terminal <NUM> of electromagnet <NUM> may be connected to a 12V power source while second terminal <NUM> of electromagnet <NUM> is connected to ground. To actuate latch pin <NUM> to the retracted position, the polarity of these connections may be reverse: first terminal <NUM> may be connected to ground while second terminal <NUM> is connected to a 12V power source. An H-bridge circuit would typically be used to implement that functionality. However, the present teachings provide circuits that allow second terminal <NUM> to always be grounded while still allowing electromagnet <NUM> to be powered with a DC current that is selectively either in a forward or a reverse direction.

<FIG> provides a drawing of a circuit <NUM> through which a plurality of electromagnets <NUM> may be powered in the desired manner. Circuit <NUM> includes impulse generator <NUM>, half bridge circuit 302A, and half bridge circuit 302B, which together form actuator control system <NUM>. When coupled to 12V DC power source <NUM>, actuator control system <NUM> is operative to provide pulses of DC current in either a forward or a reverse direction to the electromagnets <NUM> in either a first group 307A or a second group 307B. In this example, the first group 307A corresponds to the valves for a first engine cylinder and the second group 307B the valves of a second engine cylinder. Accordingly, four valves associated with one or the other engine cylinder may be activated or deactivated simultaneously. The number of electromagnet groups, the way the electromagnets are grouped, and the number of electromagnets in each group may all be varied.

Impulse generator <NUM> is an inverting DC/DC converter. As used in the present disclosure, an inverting DC-to-DC converter is any electronic device that when powered by a DC current having a first polarity is operative to provide a DC current having second polarity, which is opposite that of the first. Impulse generator <NUM> includes capacitor <NUM> and switches 305A, 305B, and 305C. Capacitor <NUM> is charged by turning switches 305A and 305B on while keeping switch 305C off. While capacitor <NUM> is charging, actuator control system <NUM> supplies DC current in a first direction be transmitting that current from power source <NUM>. When switches 305A and 305B are off and switch 305C is on, capacitor <NUM> discharges to supply DC current in the second direction.

<FIG> provides plots illustrating the operation of impulse generator <NUM> and half bridge circuit 302A, and by extension, half bridge circuit 302B. The upper plot shows the switching pattern. The lower plot shows the time variation in voltage on the left hand side of capacitor <NUM> and of current provided actuator control system <NUM>. During the initial period "I", all the switches are off and there is no current flow. For period "II", switches 305A, 305B, and 306A are on. Turning switch 306A on results in actuator control system <NUM> providing a positive current. Turning switches 305A and 305B on results in capacitor <NUM> being charged. For period "III", switch 306A is off. Switches 305A and 305B remain on and capacitor <NUM> continues to charge to the extent it is not fully charged already. Optionally, switches 305A and 305B are cycled on and off whenever capacitor <NUM> is charging to regulate its charging rate.

For period "IV" switches 305A, 305B, and 306A are off. Switches 305C and 306B are on. Switch 305C connects one side of capacitor <NUM> to ground <NUM>. As capacitor <NUM> discharges, it pulls a negative current through switch 306B. As shown in <FIG>, voltages on the left-hand side of capacitor <NUM> remain above ground. But voltages on the right-hand side of capacitor <NUM>, and by extension at terminals <NUM> of electromagnets <NUM>, are pulled below ground.

The magnitude of the negative current diminishes over period "IV". Capacitor <NUM> is sized to ensure that the current is sufficient to actuate a set of latches <NUM>. Making the largest number of electromagnets in a group smaller would reduce the required size of capacitor <NUM>. While the example shows four electromagnets per group, in some of these teachings the number of electromagnets <NUM> per group <NUM> is limited to two. In some of these teachings, the number of electromagnets <NUM> per group <NUM> is limited to one. For period "V", switches 305C and 306B are off, switches 305A and 305B are on, and capacitor <NUM> is once again charged.

<FIG> is a finite state machine diagram illustrating an example method of operating valvetrain <NUM> using latch control module <NUM>. At the center is state <NUM>, which may be the default state when valvetrain <NUM> is operating. In state <NUM>, switches 305A are 305B are on and capacitor <NUM> is charging. All other switches are off.

A command to deactivate Cylinder <NUM> causes a transition to state <NUM>. The transition may be delayed until all the rocker arm assemblies <NUM> associated with Cylinder <NUM> are within a switching window. A switching window may be a period in which latching or unlatching may be completed while all the cams operating on the rocker arm assemblies <NUM> are on base circle. In state <NUM>, switch 306A is on. Optionally, switches 305A and 305B are kept on allowing capacitor <NUM> to continue to charge. All other switches are off. State <NUM> causes the latches <NUM> of the rocker arm assemblies <NUM> that control actuation of Cylinder <NUM>'s valves (not shown) to be disengaged, which deactivates Cylinder <NUM>. After actuation is complete, latch control module <NUM> returns to the default state <NUM>. The return to state <NUM> may be based on elapsed time or in any other suitable way. In some of these teachings, the return occurs within <NUM> second or less. Preferably, the return occurs within <NUM> seconds or less. More preferably, the return occurs without <NUM> seconds or less. State <NUM> is a counterpart to state <NUM> for deactivating Cylinder <NUM>. State <NUM> is the same as state <NUM> except that switch 303A is on. Optionally, switches 305A and 305B are kept on allowing capacitor <NUM> to continue to charge.

A command to activate Cylinder <NUM> causes a transition to state <NUM>. In state <NUM>, switches 305C, and 306B are on. All other switches are off. State <NUM> causes the latches <NUM> of the rocker arm assemblies <NUM> that control actuation of Cylinder <NUM>'s valves to be re-engaged, which activates Cylinder <NUM>. After actuation is complete, latch control module <NUM> again returns to the default state <NUM>. State <NUM> is a counterpart to state <NUM> for reactivating Cylinder <NUM>. State <NUM> is the same as state <NUM> except that switch 303B is on and switch 306B is off.

Claim 1:
A valvetrain (<NUM>) for an internal combustion engine of a type that has a combustion chamber, a moveable valve having a seat formed in the combustion chamber, and a camshaft, the valvetrain (<NUM>) comprising:
a plurality of rocker arm assemblies (<NUM>), each comprising a rocker arm (103A, 103B), a latch pin (<NUM>), and a cam follower (<NUM>) configured to engage a cam mounted on a camshaft as the camshaft rotates;
a plurality of electromagnets (<NUM>) each having first and second terminals (<NUM>, <NUM>) and each operative to actuate a distinct one of the latch pins (<NUM>); and
an actuator control system (<NUM>) operative to provide the first terminal (<NUM>) of one of the electromagnets or the first terminals (<NUM>) of any selected one of a plurality of distinct groups comprising one or more of the electromagnets (<NUM>) with a DC current that is selectively either in a first direction or a second direction;
wherein the second direction is the reverse of the first.
wherein the actuator control system (<NUM>) comprises an impulse generator (<NUM>) having switching elements (305A, 305B, 305C) and one or more capacitors (<NUM>) operative to provide the current in the second direction, wherein the impulse generator (<NUM>) is an inverting DC/DC converter powered by a DC current having a first polarity to provide a DC current having a second polarity opposite that of the first.