OBD based on magnetic circuit feedback

Abstract

A method of operating an internal combustion engine that includes a valvetrain having a rocker arm assembly including a rocker arm on which a latch pin is mounted. An actuator for the latch pin, including an electromagnet, is mounted separately from the rocker arm. Rocker arm position information is obtained by gathering and analyzing data relating to a current or voltage in an electrical circuit that is operative to power the electromagnet. The rocker arm position information is used to perform a diagnostic.

Claims

1. A method of operating 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 on which a cam is mounted, and a rocker arm assembly having a rocker arm and a cam follower configured to engage the cam as the camshaft rotates, the method comprising: providing a latch assembly comprising a latch pin on the rocker arm and an actuator; wherein actuator comprises an electromagnet operative to cause the latch pin to translate between a first position and a second position and the actuator is mounted to a component distinct from the rocker arm; measuring current or voltage in an electrical circuit comprising the electromagnet to obtain data; analyzing the data to obtain rocker arm position information; performing a diagnostic based on the rocker arm position information; and reporting a result of the diagnostic to a user or technician.

2. The method of claim 1, wherein the electromagnet is operative to cause the latch pin to translate between the first and the second position by generating magnetic flux that follows a magnetic circuit that includes the latch pin.

3. The method of claim 2, wherein: the magnetic circuit includes an air gap between the latch pin and a pole piece of the actuator; and the rocker arm assembly and the latch assembly are structured such that the air gap varies in width in relation to a motion of the rocker arm that actuates the moveable valve.

4. The method of claim 2, wherein the magnetic flux passes through the rocker arm.

5. The method of claim 1, wherein the diagnostic determines one or more of whether there is wear in one or more valve lift components, whether there is a collapsed lifter, whether valve float is occurring, and whether there is a broken valve spring.

6. The method of claim 1, wherein the rocker arm has a structure that completes a magnetic circuit that makes the electromagnet operative to cause the latch pin to translate between the first position and the second position.

7. The method of claim 1, wherein: the engine comprises a pivot providing a fulcrum for the rocker arm; the pivot, the actuator, and the rocker arm assembly are structured and positioned to make the electromagnet operable to cause the latch pin to translate between the first position and the second position through magnetic flux that passes through the pivot.

8. The method of claim 1, wherein: the engine comprises a cylinder head and one or more parts including a valve cover that define an enclosed space between the valve cover and the cylinder head; and a pole piece of the actuator is located between the latch pin and an edge of the enclosed space nearest the latch pin.

9. The method of claim 1, wherein the rocker arm is configured to move independently from the electromagnet.

10. The method of claim 1, wherein the electromagnet is mounted to a component of the engine that is in a fixed position relative to the combustion chamber.

11. The method of claim 1, further comprising: pulsing the electrical circuit with a pulse insufficient in amplitude or duration to actuate the latch pin; wherein the current or voltage is induced by the pulse.

12. The method of claim 1, wherein: the current or voltage is sustained over a cam cycle; and the current or voltage does not actuate the latch pin.

13. The method of claim 1, further comprising: powering the electrical circuit with a DC current configured to actuate the latch pin; and powering the electrical circuit with an AC current while gathering the data.

14. A method of operating 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 on which a cam is mounted, a rocker arm assembly having a rocker arm and a cam follower configured to engage the cam as the camshaft rotates, the method comprising: providing a latch assembly comprising a latch pin on the rocker arm and an actuator; wherein actuator comprises an electromagnet operative to cause the latch pin to translate between a first position and a second position and the actuator is mounted to a component distinct from the rocker arm; powering the electromagnet via an electrical circuit; measuring current or voltage in the electrical circuit so as to provide circuit data; analyzing the circuit data to make one or more determinations regarding a position or movement of the rocker arm; and reporting the one or more determinations to a user or technician.

15. The method of claim 14, wherein the reporting of the one or more determinations comprises recording a diagnostic code in a data storage device or illuminating a warning light.

16. The method of claim 14, further comprising: pulsing the electrical circuit with a pulse insufficient in amplitude or duration to actuate the latch pin; wherein the current or voltage results from the pulse.

17. The method of claim 14, wherein: the electromagnet is operative to cause the latch pin to translate between the first and the second position by generating magnetic flux that follows a magnetic circuit that includes the latch pin; the magnetic circuit includes an air gap between the latch pin and a pole piece of the actuator; and the rocker arm assembly and the latch assembly are structured such that the air gap varies in width in relation to a motion of the rocker arm that actuates the moveable valve.

18. The method of claim 14, wherein the electromagnet is mounted to a component of the engine that is in a fixed position relative to the combustion chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a partial cross-section of an internal combustion engine with a valvetrain according to some aspects of the present teachings.

(2) FIG. 1B is the same view as FIG. 1A, but with the latch pin moved from an engaging to a non-engaging position.

(3) FIG. 1C is the same view as FIG. 1A, but with the cam risen off base circle.

(4) FIG. 1D is the same view as FIG. 1B, but with the cam risen off base circle.

(5) FIG. 1E illustrates a modification of the valvetrain in FIG. 1A according to some aspects of the present teachings.

(6) FIG. 2A provides a perspective view of a portion of the valvetrain of the engine illustrated by FIG. 1A.

(7) FIG. 2B provides the same view as FIG. 2A, but with the latch pins moved from engaging to non-engaging positions.

(8) FIG. 3A provides a perspective view of an actuator mounting frame according to some aspects of the present teachings, which is used in the valvetrain of FIG. 2A.

(9) FIG. 3B provides an explode view of the mounting frame of FIG. 3A.

(10) FIG. 3C provide a perspective view of four actuators 127A according to the present teachings incorporating the mounting frame of FIG. 3A.

(11) FIG. 4 provides a perspective view of a valvetrain according to some aspects of the present teachings with a pole piece shown in transparency.

(12) FIG. 5 is a partial cross-section of an internal combustion engine according to some aspects of the present teachings including a cross-section of the valvetrain of FIG. 4 through one of the rocker arm assemblies of that valvetrain.

(13) FIG. 6 is a perspective view of an actuator used in the valvetrain of FIG. 4.

(14) FIG. 7 is a cross section taken through the line 7-7 of FIG. 5.

(15) FIG. 8 is a perspective view of a portion of the engine of FIG. 5 showing some parts in transparency and illustrating a magnetic circuit according to some aspects of the present teachings.

(16) FIG. 9 is a flow chart of a method of operating an internal combustion engine according to some aspects of the present teachings.

(17) FIG. 10 is a flow chart of a diagnostic method according to some aspects of the present teachings.

DETAILED DESCRIPTION

(18) 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, valvetrain 101 is the same as valvetrain 101A, 101B.

(19) FIG. 1A provides a partial-cutaway side view of a portion of an engine 100A including a valvetrain 101A in accordance with some aspects of the present teachings. Engine 100A includes a cylinder head 130 in which a combustion chamber 137 is formed, a moveable valve 185 having a seat 186 formed within combustion chamber 137, and a camshaft 169 on which a cam 167 is mounted. Moveable valve 185 may be a poppet valve. Valvetrain 101A includes rocker arm assembly 115A, hydraulic lash adjuster (HLA) 181, and latch assembly 105A. Rocker arm assembly 115A includes rocker arm 103A (an outer arm) and rocker arm 103B (an inner arm). HLA 181 is an example of a pivot. It provides a fulcrum on which rocker arm 103A pivots. A pivot may alternatively be a mechanical lash adjuster, a post that provides a fulcrum on which a rocker arm pivots, or a rocker shaft. Outer arm 103A and inner arm 103B are pivotally connect through shaft 149. A cam follower 107 may be mounted to inner arm 103B through bearings 165 and shaft 147. Cam follower 107 is configured to engage cam 167 as camshaft 169 rotates. Cam follower 107 is a roller follower but could alternatively be another type of cam follower such as a slider.

(20) Shaft 147 protrudes outward through openings 182 in the sides of outer arm 103A to engage torsion springs 145 (see FIG. 2A), which are mounted to outer arm 103A. If inner arm 103B pivots downward relative to outer arm 103A on shaft 149 as shown in FIG. 1D, torsion springs 145 act on shaft 147 to drive inner arm 103B to pivot back toward the position shown in FIG. 1A.

(21) Latch assembly 105A includes an actuator 127A mounted to HLA 181 and a latch pin 114A mounted on rocker arm 103A. In this specification, the terms latch pin and rocker arm encompass the most basic structures that would be commonly understood as constituting a latch pin or a rocker arm and may further encompass parts that are rigid and rigidly held to that most basic structure. A rocker arm assembly is operative to form one or more force transmission pathways between a cam and a moveable valve. A rocker arm is a lever operative to transmits force from the cam along one or more of those pathways. The most basic structure of the rocker arm, which is its core structure, is capable of bearing the load and carrying out that function.

(22) Latch pin 114A is translatable between a first position and a second position. The first position may be an engaging position, which is illustrated in FIG. 1A. The second position may be a non-engaging position, which is illustrated in FIG. 1B. A spring 141 mounted within outer arm 103A may be configured to bias latch pin 114A into the engaging position. 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.

(23) FIG. 1C shows the effect if cam 167 rises off base circle while latch pin 114A is in the engaging position. Latch pin 114A may engage lip 109 of inner arm 103B, after which inner arm 103B and outer arm 103A may be constrained to move in concert. HLA 181 may provide a fulcrum on which inner arm 103B and outer arm 103A pivot together as a unit, driving down on valve 185 via an elephant's foot 151, compressing valve spring 183 against cylinder head 130, and lifting valve 185 off its seat 186 within combustion chamber 137 with a valve lift profile determined by the shape of cam 167. The valve lift profile is the shape of a plot showing the height by which valve 185 is lifted of its seat 186 as a function of angular position of camshaft 169.

(24) FIG. 1D shows the effect if cam 167 rises off base circle while latch pin 114A is in the non-engaging position. Cam 167 still drives inner arm 103B downward, but instead of compressing valve spring 183, inner arm 103B pivots on shaft 149 against the resistance of torsion springs 145. Torsion springs 145 yield more easily than valve spring 183. Outer arm 103A remains stationary and valve 185 remains on its seat 186. Accordingly, the non-engaging configuration may provide deactivation of a cylinder with a port controlled by valve 185. Alternatively, there may be additional cams that operate directly on outer arm 103A. These additional cams may provide a lower valve lift profile than cam 167. 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.

(25) Actuator 127A may include an electromagnet 119 and pole pieces 131A and 131B. As the term is used in this disclosure, a pole piece may be any part formed of low coercivity ferromagnetic material and located in a position where it is operative to complete a magnetic circuit. Actuator 127A is mounted to HLA 181 through pole piece 131A, which also provides a core for electromagnet 119. HLA 181 includes an inner sleeve 175 and an outer sleeve 173. Outer sleeve 173 is installed within a bore 174 formed in cylinder head 130. Outer sleeve 173 may rotate within bore 174, but is otherwise substantially stationary with respect to cylinder head 130. Inner sleeve 175 is telescopically engaged within outer sleeve 173 and provides a fulcrum on which outer arm 103A pivots. That fulcrum may be hydraulically raised or lowered to adjust lash.

(26) Latch pin 114A, outer arm 103A, inner sleeve 175, and outer sleeve 173 may be made entirely of low coercivity ferromagnetic material. Together with pole pieces 131A and 131B, they may form a magnetic circuit 220E, which is shown in FIG. 1B. A magnetic circuit is a structure operative to be the pathway for an operative portion of the magnetic flux from a magnetic flux source. Magnetic circuit 220E provides a pathway for magnetic flux that is generated by electromagnet 119. The magnetic flux that is generated by electromagnet 119 and follows magnetic circuit 220E is operative to actuate latch pin 114A from its engaging to its non-engaging position. When electromagnet 119 is first energized, magnetic circuit 220E includes the air gap 134A, which is shown in FIG. 1A. Energizing electromagnet 119 generates magnetic flux that polarizes low coercivity ferromagnetic materials within circuit 220E and results in magnetic forces on latch pin 114A that tend to drive it to the non-engaging position shown in FIG. 1B. Driving latch pin 114A to the non-engaging configuration reduces air gap 134A and the magnetic reluctance in circuit 220E. If electromagnet 119 is switched off, spring 141 may drive latch pin 114A back into the engaging configuration and reopen air gap 134A.

(27) Magnetic circuit 220E passes through rocker arm 103A. In this disclosure, passing through a part means passing through the smallest convex volume that can enclose the part. When asserting that a magnetic flux that is operative passes through a part, the meaning is that the entirety of a portion of the magnetic flux that is sufficient to be operative passes through that part. In other words, the operability is achieved independently from any flux that follows a circuit that does not pass through the part.

(28) Magnetic circuit 220E passes through the structure of rocker arm 103A. Passing through the structure of a part means passing through the material that makes up that part. If the part forms a low reluctance pathway for the magnetic flux, it may help define the magnetic circuit. Low coercivity ferromagnetic materials in particular are useful in establishing magnetic circuits. In some cases, the magnetic properties of a part are essential to the formation of a magnetic circuit through which actuator 127 is operative. A touchstone for these cases is that if that part were replaced by an aluminum part, an operability dependent on that circuit would be lost. Aluminum is an example of a paramagnetic material. For the purposes of this disclosure, a paramagnetic material is one that does not interact strongly with magnetic fields.

(29) HLA 181 and latch pin 114A form essential parts of magnetic circuit 220E. In other words, if either of these parts were replaced by ones made entirely of aluminum, actuator 127 would cease to be operative to actuate latch pin 114A. Depending on the strength of electromagnet 109, the core structure of rocker arm 103A may also form an essential part of magnetic circuit 220E. Rocker arm 103A may be formed of low coercivity ferromagnetic material that provides a low reluctance pathway for magnetic flux crossing from HLA 181 to latch pin 114A. On the other hand, HLA 181 brings magnetic flux sufficiently close to latch pin 114A that magnetic flux may cross between HLA 181 and latch pin 114A following magnetic circuit 220E regardless of the material in between. In some of these teachings, pole pieces 192L are positioned to the sides of rocker arm 103A as illustrated in FIG. 1E to facilitate transmission of magnetic flux from HLA 181 to latch pin 114A within rocker arm 103A.

(30) Latch pin 114A, by virtue of being mounted to outer arm 103A, has a range of motion relative to combustion chamber 137 and actuator 127A. This range of motion may be primarily the result of outer arm 103A pivoting on HLA 181 when rocker arm assembly 115A is in the engaging configuration. On the other hand, the position of latch 117A relative to actuator 127A may be substantially fixed while latch 117A is in the non-engaging configuration. Extension and retraction of HLA 181 may introduce some relative motion, but excluding a brief period during start-up, the range of motion introduced by HLA 181 may be negligible. As long as latch pin 114A is in the non-engaging configuration, magnetic circuit 220E may remain operative whereby electromagnet 119 may act through that circuit to maintain latch pin 114A in the non-engaging configuration.

(31) FIGS. 2A and 2B are perspective views of a portion of the valvetrain 101A, which is in accordance with some aspects of the present teachings and is a part of engine 100A. As shown by these illustrations, actuator 127A may be one of four supported by a common mounting frame 123. The four actuators 127A may control two intake ports and two exhausts ports for one engine cylinder. Mounting frame 123 may include four pole pieces 131A joined with a paramagnetic connecting structure 122.

(32) As shown in FIGS. 3A-3C, mounting frame 123 may join with an upper frame 125 to support and protect a wiring harness 124. Wiring harness 124 includes wires 128 that provide power to electromagnets 119. Mounting frame 123 supports wiring harness 124 from below. Upper frame 125 may protect wires 128 from objects falling from above during manufacturing or maintenance. Upper frame 125 may include four pole pieces 131B and a paramagnetic connecting structure 129.

(33) Wires 128 may all connect to a common plug 126. In some of these teachings, two of the electromagnets 119 are connected in series or in parallel. In some of these teachings, all four of the electromagnets 119 are connected in series or in parallel. These options reduce the number of wires in plug 126 and allowing a tradeoff between circuit costs and flexibility. For example, the intake and exhaust valves in a multi-valve engine may only be subject to deactivation in pairs. In some of these teachings, a plurality of electromagnets 119 share a common ground connection. In some of these teachings, one or more electromagnets 119 are grounded through cylinder head 130.

(34) In accordance with some of the present teachings, mounting frame 123 is supported to two or more HLAs 181 that are angled with respect to one another when installed in their bores 174. This angling may restrict vertical movement of mounting frame 123. Mounting frame 123 may not fit over HLAs 181. In an installation method, two or more HLAs 181 may be slid through openings in mounting frame 123 into their bores 174. Electromagnets 119 and wiring harness 124 may be installed on mounting frame 123 either before or after this operation. Upper frame 125 may be connected to mounting frame 123 any time after the installation of electromagnets 119. Mounting frame 123 may be further secured with connectors attaching frame 123 to cylinder head 130.

(35) Rather than being supported on HLAs 181, mounting frame 123 may be supported by cylinder head 130. Mounting frame 123 may still abut HLAs 181, whereby HLAs 181 facilitate proper position of the pole pieces 131 on mounting frame 123. In addition, mounting frame 123 may include a circular opening 132 that is shaped to fit around a spark plug tower (not shown). The spark plug tower may then also be used to achieve correct and stable positioning of pole pieces 131.

(36) Mounting frame 123 may be part of a valve actuation module. In the present disclosure, a valve actuation module is a structure that includes a rocker arm assembly 115 and an actuator 127 according to the present disclosure. The actuator 127 may be mounted to a pivot for the rocker arm assembly 115. For example, the actuator 127 may be mounted to an HLA 181. In some of these teachings, the HLA 181 and the rocker arm assembly 115 are held together by a removable clip (not shown). The clip may hold HLA 181 and rocker arm assembly 115 together during shipping and through installation of valve actuation module within an engine 100.

(37) FIG. 4 provides a perspective view of a portion of a valvetrain 101B according to some other aspects of the present teachings. Valvetrain 101B may be used in place of valvetrain 101A in engine 100A. FIG. 5 provides a cross-sectional view of what valvetrain 101B would look like in engine 100A. Valvetrain 101B may be the same as valvetrain 101A except that valvetrain 101B uses one or more latch assemblies 105B in place of one or more latch assemblies 105A. Latch assembly 105B includes actuator 127B and two latch pins 114B.

(38) FIG. 6 illustrates the parts of actuator 127B separately from other components of valvetrain 101B. Actuator 127B includes pole piece 131C, pole piece 131D, and electromagnet 119. Pole piece 131C may provide a core for electromagnet 119 and may be mounted to a pair of HLAs 181. Pole piece 131D may be mounted separately from pole piece 131C. As shown in FIGS. 4 and 5, pole piece 131D may be positioned between latch pins 114B and an outer portion of engine 101A, such as cylinder head 130. Pole piece 131D forms a low reluctance pathway for magnetic flux between two latch pins 114B. Pole piece 131D may be mounted to cylinder head 130.

(39) Actuator 127B places electromagnet 119 between two adjacent rocker arm assemblies 115A. When electromagnet 119 is energized, it actuates the two latch pins 114B to their non-engaging position through magnetic flux that follows the magnetic circuit 220F illustrated in FIG. 7. Magnetic circuit 220F includes pole pieces 131C and 131D, two HLAs 181, two outer arms 103A, and two latch pins 114B. Magnetic flux from electromagnet 119 following magnetic circuit 220F proceeds from electromagnet 119 through pole piece 131C to one of the HLAs 181, up the HLA 181, through the associated rocker arm 103A, through the latch pin 114B mounted to that rocker arm 103A, across an air gap 134B to pole piece 131D, through pole piece 131D, across another air gap 134B to the other latch pin 114B, through the other rocker arm 103A, down through the other HLA 181, back into the pole piece 131C, and from there back to electromagnet 119. The magnetic flux polarizes low coercivity ferromagnetic materials throughout the circuit 220F and place magnetic force on latch pins 114B that causes them to actuate to the non-engaging position, narrowing the air gaps 134B in the process.

(40) Referring to FIG. 5, latch pin 114B is held within a chamber 177 of rocker arm 103A by a latch pin cage 110. Chamber 177 may have been originally designed to operate as a hydraulic chamber. In some of the present teachings, latch pin cage 110 is paramagnetic, which may improve the operation of latch assembly 105B. Latch pin cage may be press fit into chamber 177 or otherwise secured to prevent rotation with respect to rocker arm 103A. Referring to FIGS. 5 and 7, at one or the other end of chamber 177, there is an opening 180 through which latch pin 114B extends. In some of the present teachings, latch pin 114B has a non-circular profile where it passes through opening 180 and the shape of opening 180 cooperates with the profile of latch pin 114B to restrict rotation of the latch pin 114B. In this example, opening 180 has a D-shape and latch pin 114B has a mating D-shaped profile. In this way, latch pin 114B may be installed in chamber 177 with latch pin cage 110 providing an anti-rotation guide feature.

(41) In accordance with some of the present teachings, latch pin 114B has an expanded end 111 that does not fit within the opening in rocker arm 103A out of which latch pin 114B extends. Expanded end 111 has a larger cross-sectional area than the core 113B of latch pin 114B that travels within hydraulic chamber 177. The large cross-sectional area of end 111 facilitates its interaction with pole piece 131D. In accordance with some of these teachings, pole piece 131D is mounted to be facing end 111 when cam 167 is on base circle. The facing surfaces may be parallel or nearly parallel. In some of these teachings, the facing surfaces are generally flat. In some of these teachings, latch pin 114 contacts an actuator pole piece 131 when latch pin 114 is in the non-engaging position. In some of these teachings, one or both of the contacting surfaces has one or more dimples. Dimples may be operative to prevent end 111 and pole piece 131D from contacting over a large surface area and potentially sticking together. In some of these teachings the facing surfaces are parallel or nearly parallel to a direction of lash adjustment provided by lash adjuster 181. This geometry may facilitate maintaining operability of actuator 127B over a range of lash adjustment.

(42) The rocker arms 103 of the examples herein are all rocker arms that have been put into production for use with a hydraulically actuated latch. For example, with reference to FIG. 1A, latch pin 114A is installed within a hydraulic chamber 177 of rocker arm 103A. The surface 178 through which rocker arm 103A contacts hydraulic lash adjuster 181 is shaped to form a hydraulic seal with lash adjuster 181. In some of these teachings, rocker arm assembly 115 includes a dual feed hydraulic lash adjuster 181 that was put into production for use with a hydraulically latching rocker arm. Hydraulic lash adjuster 181 may include a port 179 configured to channel hydraulic fluid from cylinder head 130 to rocker arm 103A. For hydraulic operation, a port for hydraulic fluid is formed by drilling a hole in rocker arm 103A from surface 178 into hydraulic chamber 177. That is a post-production step that need not be carried out when rocker arm 103A is used for electromagnetic latching as described herein.

(43) FIG. 9 provides a flow chart of a method 300 that may be used to operate an engine 100 with a valvetrain 101. Method 300 may begin with act 301, rotating camshaft 169. Rotating camshaft 169 may be inherent in running engine 100. Act 303 checks whether cam 167 is on base circle. Act 303 may be used to ensure that latch pin 114 is actuated only when cam 167 is on base circle. Rather than simply limit the start of actuation to times when cam 167 is on base circle, act 303 may more narrowly limit the range of camshaft phase angles at which latch pin actuation may be initiated to ensure that actuation is complete before cam 167 begins to rise off base circle. Act 305 determines whether an unlatch command, such as a command to deactivate valve 185, is currently in force. If yes, method 300 proceeds with act 307, powering electromagnet 119 to actuate latch pin 114 if latch pin 114 is not already in the non-engaging position. If no and latch pin 114 is not already in the engaging position, method 300 proceeds with act 309 to deactivate electromagnet 119 thereby allowing latch pin 114 to actuate to the engaging position under the influence of spring 141 or the like.

(44) In some aspects of the present teachings, act 307 generates magnetic flux that enters rocker arm 103A and actuates a latch pin 114 mounted on that rocker arm. Magnetic flux follows closed loops, so the flux that enters rocker arm 103A also leaves rocker arm 103A before returning to its source. In some of the present teachings, the flux that enters and leaves rocker arm 103A is sufficient to result in latch pin 114 actuating. The source of magnetic flux may be relatively stationary with respect to combustion chamber 137. Rocker arm 103A, on the other hand, is mobile with respect to combustion chamber 137. In some of these teachings, act 307 places a magnetic force directly on the latch pin 114. This force may initially actuate the latch pin 114 and subsequently maintain the position of latch pin 114 while engine 100 continues to operate through act 301.

(45) Act 307 may power electromagnet 119 with either an alternating current (AC) or a direct current (DC). In some of these teachings, act 307 powers electromagnet 119 with a DC current. In some of these teachings deactivating electromagnet 119 cuts power to electromagnet 119 entirely. But in some of these teachings, deactivating electromagnet 119 simply reduces the current or changes it in such a way that latch pin 114 ceases to be held in the non-engaging position.

(46) FIG. 9 provides a flow chart of an example method 310 according to some aspects of the present teachings. Method 310 may be used with valvetrain 101A, valvetrain 101B, or any other valvetrain in which a latch pin 114 mounted to rocker arm 103A is actuated using an electromagnet 119 operating through a magnetic circuit 220 having an air gap 134 that varies in width in relation to a motion of rocker arm 103A that actuates a poppet valve 185. Method 310 may be carried out simultaneously with method 300 and includes act 301, which has camshaft 169 in a state of rotation.

(47) Act 311 is driving a circuit that includes electromagnet 119 to facilitate data collection. Driving the circuit may include pulsing the circuit. In some examples, a DC current pulse may be used. The default position for latch pin 114 could be either the engaging or the non-engaging configuration. A DC pulse could be applied on top of a DC current that is used to hold latch pin 114 in position. But in some of these teachings, the DC pulse is applied only when electromagnet 119 is not energized. In some examples, an AC current is applied to facilitate data collection while a DC current is used to actuate latch pin 114.

(48) In some of these teachings, a circuit including electromagnet 119 is driven continuously over extended periods in a way that enables the data collection of act 313 but does not affect the position of latch pin 114. The current provided for data collection may be AC or DC. The periods may be in excess of the time taken for camshaft 169 to complete a rotation. In some examples, the current applied to facilitate data collection is insufficient in magnitude or duration to actuate latch pin 114. In some examples, the current applied to facilitate data increases the amount of force holding latch pin 114 in its current position.

(49) Act 313 is data collection, which may take place while the circuit is being driven according to act 311. Data collection may include measuring a current or voltage in an electrical circuit comprising electromagnet 119. A time variation in that current or voltage may be measured. The data may be obtained using any suitable measuring device. Examples of measuring devices that may be suitable include, without limitation, a shunt resistor and a Hall effect sensor.

(50) In an alternative provided by the present disclosure, the electrical circuit including electromagnet 119 is monitored passively, making action 311 optional. If there is magnetic flux in a circuit comprising electromagnet 119, any expansion or contraction of air gap 134 will produce a change in that flux and induce a current in electromagnet 119. That induced current may be detected and analyzed to determine the change in air gap 134. In some of these teaching, a permanent magnet is configured to continuously maintain a magnetic flux in a magnetic circuit comprising electromagnet 119. That flux may be insufficient to hold latch pin 114 in any particular position.

(51) Act 315 is using the collected data to obtain position information for rocker arm 103A. An instantaneous rocker arm position may be determined. Alternatively, a set representing data collected over a span of time may be analyzed to determine, for example, a valve lift profile. The data will depend on the inductance of the circuit, which will depend on the inductance of electromagnet 119, which will depend on the magnetic reluctance of magnetic circuit 220, which will depend on the size of air gap 134, which will depend on the pivot angle of rocker arm 103A on the fulcrum provided by HLA 181, which determines the amount by which valve 185 has been lifted of its seat 186. Analyzing the data may include one or more of comparing the data to results obtained during calibration, comparing the data to model predictions, comparing the data to data obtained during a previous cam cycle, comparing the data to data obtained at other cam phases, and comparing similar data obtained from other rocker arms.

(52) The size of air gap 134 is also affected by the position of latch pin 114. Therefore, method 310 may be modified or extended to provide a determination of whether latch pin 114 is in the extended or retracted position. In some of these teachings, information obtained from the circuit comprising electromagnet 119 is used to distinguish among three states. In the first state, latch pin 114 is in the non-engaging configuration. In the second state, latch pin 114 is in the engaging configuration and cam 167 is on base circle. In the third state, latch pin 114 is in the engaging configuration and cam 167 is off base circle. The determination of the third state may further include a determination of rocker arm position.

(53) Act 317 is performing an operation using the rocker arm position information derived in act 315. In some of these teachings, the operation of act 317 is a diagnostic. A diagnostic operation may include a reporting step. The report may be made selectively. The report may be sending a signal, such as illuminating a warning light. In some of these teachings, the diagnostic operation includes recording a diagnostic code in a data storage device. The diagnostic code may later be read by a technician.

(54) Some of the diagnostic determinations that may be made using the rocker arm position data include determining whether there is wear in one or more valve lift components, determining whether there is a collapsed lifter, determining whether valve float is occurring, and determining whether there is a broken valve spring. Some of these diagnostics may involve making several rocker arm position determinations to obtain sufficient information relating to a current valve lift profile. Some of these diagnostics may involve observing a variation in valve lift profile over time.

(55) In some of these teachings, method 310 or one of the variations thereof described above is used to detect a critical shift in rocker arm assembly 115A. A critical shift is the case where latch pin 114 comes out of the engaging position while cam 167 is lifting rocker arm 103B. If this happens, rocker arm 103A will be driven by valve spring 183 to rapidly pivot from a lifted position like the one shown in FIG. 1C to its base circle position shown in FIG. 1D. In some of these teachings, a critical shift is detected from the speed with which inductance or a related property varies. In some of these teachings, a critical shift is detected from an induced current in the circuit. In some of these teachings, a critical shift is detected from data indicating a premature return to base circle.

(56) In some of these teachings, the operation of act 317 is an engine management operation. An engine management operation is one that affects a running state of engine 100. For example, the rocker arm position information may be use in a control algorithm. In some of these teachings, the rocker arm position information is used to provide camshaft position information and the camshaft position information is used in the control algorithm. The present teaching of using rocker arm position information to obtain camshaft position information and using that camshaft position information to control an engine is independent of the method by which the rocker arm position is determined or the structure used to determine the rocker arm position. The rocker arm position may be determined using any suitable device and method.

(57) The camshaft position may be determined with greater accuracy or reliability by combining the rocker arm position information with position data from another rocker arm. The camshaft position information may be used in the same way as information from a conventional camshaft position sensor. The information may be used, for example, to determine the timing of an ignition or a fueling event. Crankshaft position information may be used in conjunction with the camshaft position information within the engine management operation. The rocker arm position information may be used to augment or substitute for the information provided by a camshaft position sensor. Here, the term camshaft position sensor is used in the sense of a device known in the industry as a camshaft position sensor.

(58) A camshaft position sensor of a conventional type provides coarse data regarding camshaft position. Rocker arm position information can provide more precise camshaft position data. That higher precision data may be enabling for certain applications. One such application is a method of operating a cylinder deactivating rocker arm assembly actuated by a two-lobe cam. The latch can be engaged and disengaged with each cam cycle whereby the valve is lifted by one of the lobes but deactivated with respect to the other lobe.

(59) The approximate shape of the valve lift profile may be known. Accordingly, as few as two data points may be sufficient to determine the rate of camshaft rotation and the current position (phase angle) of the camshaft. Greater numbers of data points may be used to perform statistical analysis to improve the accuracy of these determinations and/or refine a representation of the shape of the valve lift profile.

(60) The analysis of rocker arm position information may be used to identify one or more critical points in the cam cycle. Critical points in the cam cycle include the point at which the rocker arm begins to lift and the point at which the rocker arm completes its decent. These events are closely related to valve opening and valve closing. The point at which the rocker arm reaches maximum lift is also of interest. It may be desirable to collect rocker arm position data while the rocker arm is near the point of maximum lift to obtain measurements with a high signal to noise ratio. In some of these teachings, a determination of camshaft position is used in setting the timing for a subsequent measurement of rocker arm position.

(61) The components and features of the present disclosure have been shown and/or described in terms of certain aspects and examples. While a particular component or feature, or a broad or narrow formulation of that component or feature, may have been described in relation to only one embodiment or one example, all components and features in either their broad or narrow formulations may be combined with other components or features to the extent such combinations would be recognized as logical by one of ordinary skill in the art.