Electrically latching rocker arm assembly having built-in OBD functionality

Abstract

An internal combustion engine includes a cam-actuated rocker arm assembly with a solenoid-actuated latch that provides for cylinder deactivation or variable valve actuation. The solenoid has an inductance that varies significantly in relation to the position of a latch pin as it translates between latching and non-latching configurations. A sensor is positioned to monitor a current or a voltage in a circuit that includes the solenoid. Diagnostic information relating to the operation of the rocker arm assembly is determined by comparing data collected from the sensor over a first period to data collected from the sensor over a second period.

Claims

1. A method of providing diagnostic information for a rocker arm assembly, the method comprising: providing the rocker arm assembly with a latch pin configured to translate between a first position and a second position and a solenoid configured to actuate the latch pin, wherein an inductance of the solenoid varies with latch pin position as the latch pin translates between the first position and the second position; driving a circuit comprising the solenoid over a first interval; obtaining a first data set related to the inductance by measuring a current in the circuit during the first interval; driving the circuit over a second interval; obtaining a second data set related to the inductance by measuring a current in the circuit during the second interval; generating diagnostic information relating to location or movement of the latch pin from a comparison between the first data set and the second data set; and reporting the diagnostic information to a user or technician or recording the diagnostic information in a data storage device.

2. The method of claim 1, wherein the driving of the circuit over the first interval comprises providing the circuit with a DC voltage pulse predetermined to be sufficient to actuate the latch pin from the first position to the second position.

3. The method of claim 1, wherein: the driving of the circuit over the first interval comprises providing a first DC voltage pulse to the circuit; and the driving of the circuit over the second interval comprises providing a second DC voltage pulse to the circuit.

4. The method of claim 3, further comprising: between the first interval and the second interval, the circuit with a DC voltage pulse predetermined to be sufficient to actuate the latch pin from the first position to the second position.

5. The method of claim 3, wherein the first DC voltage pulse and the second DC voltage pulse are predetermined to be insufficient in duration or magnitude to actuate the latch pin.

6. The method of claim 1, wherein the comparison between the first data set and the second data set includes an integration involving the first data set and the second data set.

7. The method of claim 1, wherein the driving of the circuit over the first interval and the driving of the circuit over the second interval consists essentially of applying one DC voltage pulse to the circuit.

8. The method of claim 1, wherein the latch pin actuates from the first position to the second position during the first interval.

9. A method of providing diagnostic information for a rocker arm assembly, the method comprising: providing the rocker arm assembly with a latch pin configured to translate between a first position and a second position and a solenoid configured to actuate the latch pin, wherein an inductance of the solenoid varies with latch pin position as the latch pin translates between the first position and the second position; driving a circuit comprising the solenoid during a driving period with a DC voltage pulse predetermined to be sufficient to actuate the latch pin from the first position to the second position; measuring a current in the circuit over a first period to obtain a first data set, wherein the first period is before or during the driving period; measuring a current in the circuit over a second period to obtain a second data set, wherein the second period is during or after the driving period; generating diagnostic information relating to a location of the latch pin after the driving period or whether the latch pin moved from the first position to the second position during the driving period from a comparison between a first value, related to the inductance and determined from the first data set, to a second value, related to the inductance and determined from the second data set; and reporting the diagnostic information to a user or technician or recording the diagnostic information in a data storage device.

10. The method of claim 9, wherein the first value and the second value are determined from an integration involving the first data set and the second data set.

11. The method of claim 9, wherein the current in the circuit over the first period and the current in the circuit over the second period are driven by the DC voltage pulse.

12. The method of claim 9, wherein: at least one of the current in the circuit over the first period and the current in the circuit over the second period is driven by a voltage pulse that is different from the DC voltage pulse.

13. The method of claim 9, wherein: the current in the circuit over the first period is driven by a first voltage pulse that is different from the DC voltage pulse; the current in the circuit over the second period is driven by a second voltage pulse that is different from the DC voltage pulse; and the first voltage pulse and the second voltage pulse are insufficient in voltage or duration to actuate the latch pin.

14. The method of claim 9, wherein the diagnostic information determines whether the latch pin actuated from the first position to the second position in response to the DC voltage pulse.

15. A method of providing diagnostic information for a rocker arm assembly, the method comprising: providing the rocker arm assembly with a latch pin configured to translate between a first position and a second position and a solenoid configured to actuate the latch pin, wherein an inductance of the solenoid varies with latch pin position as the latch pin translates between the first position and the second position; driving a circuit comprising the solenoid during a driving period with a DC voltage pulse configured to actuate the latch pin from the first position to the second position; determining a first value related to the inductance by measuring a current in the circuit during a first period, wherein the first period is before or during the driving period; determining a second value related to the inductance by measuring a current in the circuit during a second period, wherein the second period is during or after the driving period; generating diagnostic information relating to whether the driving of the circuit resulted in movement of the latch pin from the first position to the second position by comparing the first value to the second value; and reporting the diagnostic information to a user or technician or recording the diagnostic information in a data storage device.

16. The method of claim 15, wherein the current in the circuit during the first period and the current in the circuit during the second period are driven by the DC voltage pulse.

17. The method of claim 15, wherein: at least one of the current in the circuit during the first period and the current in the circuit during the second period is driven by a voltage pulse that is different from the DC voltage pulse.

18. The method of claim 17, wherein one of the current in the circuit during the first period and the current in the circuit during the second period is driven by the DC voltage pulse.

19. The method of claim 15, wherein: the current in the circuit during the first period is driven by a first voltage pulse that is different from the DC voltage pulse; the current in the circuit during the second period is driven by a second voltage pulse that is different from the DC voltage pulse; and the first voltage pulse and the second voltage pulse are insufficient in voltage or duration to actuate the latch pin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional side view of a portion of an internal combustion according to some aspects of the present teachings including a rocker arm assembly in a non-engaging configuration and a cam on base circle.

(2) FIG. 2 provides the view of FIG. 1, but with the rocker arm assembly in an engaging configuration.

(3) FIG. 3 provides the view of FIG. 2, but with the cam risen off base circle.

(4) FIG. 4 provides the view of FIG. 1, but with the cam risen off base circle.

(5) FIG. 5 illustrates a circuit in accordance with some aspects of the present teachings.

(6) FIG. 6 is a cross-sectional side view of a portion of an internal combustion according to some aspects of the present teachings including a rocker arm assembly in an engaging configuration and a cam on base circle.

(7) FIG. 7 illustrates the valvetrain of FIG. 6 with the cam off base circle.

(8) FIG. 8 is a cross-section side view of an electromagnetic latch assembly according to some aspects of the present teachings with the latch pin in an extended position.

(9) FIG. 9 provides the same view as FIG. 8, but illustrating magnetic flux that may be generated by the solenoid.

(10) FIG. 10 provides the view of FIG. 8 but with the latch pin in a retracted position.

(11) FIG. 11 illustrates a circuit in accordance with some aspects of the present teachings

(12) FIG. 12 is a flow chart of a method of operating an internal combustion engine in accordance with some aspects of the present teachings.

(13) FIG. 13 illustrates a coil in accordance with some aspects of the present teachings.

(14) FIG. 14 is a flow chart of a method of operating an internal combustion engine in accordance with some aspects of the present teachings.

(15) FIG. 15 is a flow chart of a method of operating an internal combustion engine in accordance with some aspects of the present teachings.

(16) FIG. 16 is a flow chart of a method of operating an internal combustion engine in accordance with some aspects of the present teachings.

(17) FIG. 17 plots an example of current versus time variation in a circuit comprising a solenoid over a period following connecting the circuit to a voltage source in an attempt to actuate a latch pin.

(18) FIG. 18 plots an example of current versus time variation in a circuit comprising a solenoid over a period following connecting the circuit to a voltage source in an attempt to actuate a latch pin to a position in which the latch pin is stable.

(19) FIG. 19 plots an example of current versus time variation in a circuit comprising a solenoid over a period following connecting the circuit to a voltage source with a reverse polarity in an attempt to actuate a latch pin.

(20) FIG. 20 plots an example of current versus time variation in a circuit comprising a solenoid following decoupling the circuit from a voltage source.

(21) FIG. 21 is a flow chart of a method of operating an internal combustion engine in accordance with some aspects of the present teachings.

DETAILED DESCRIPTION

(22) 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, internal combustion engine 117 is the same as internal combustion engine 117A, 117B. Internal combustion engine 117 is therefore a generic reference that includes the specific instances internal combustion engine 117A and internal combustion engine 117B. Where options are provided for one instance subject to a generic reference, those options are to be given consideration in connection with all instances subject to that generic reference.

(23) FIGS. 1-4 illustrate an internal combustion engine 117A in accordance with some of the present teachings. Referring to FIG. 1, internal combustion engine 117A includes cylinder head 103 and valvetrain 115A. Valvetrain 115A includes poppet valve 106, which has a seat 102 within cylinder head 103, cam shaft 125, on which is mounted eccentrically shaped cam 127, and rocker arm assembly 147A. Rocker arm assembly 147A may include inner arm 111A, to which cam follower 119 is mounted, outer arm 111B, and hydraulic lash adjuster 165. Both rocker arms 111 are mobile relative to cylinder head 103. Cam follower 119 may be a roller follower and is configured to engage cam 127 as cam shaft 125 rotates. Rocker arm assembly 147A is operative to transmit force from cam 127 to actuate valve 106.

(24) A solenoid 139, which is part of an electromagnetic latch assembly 150A, is mounted to outer arm 111B. Electromagnetic latch assembly 150A may further include a spring 141 and a latch pin 133. Latch pin 133 may be formed of a low coercivity ferromagnetic material such as soft iron. Alternatively, a low coercivity ferromagnetic part such as annular ring 135 may be mounted to latch pin 133. Latch pin 133 is translatable between extended and retracted positions. Spring 141 may bias latch pin 133 toward the extended position, which is shown in FIG. 2. Solenoid 139 may be operative when energized to exert a magnetic force on low coercivity ferromagnetic ring 135 and draw latch pin 133 to the retracted position, which is shown in FIG. 1. A shell 137 of low coercivity ferromagnetic material may be formed around solenoid 139 to provide a low reluctance pathway for magnetic flux from solenoid 139 and thereby increase the force of its action on latch pin 133.

(25) The extended position for latch pin 133 may be described as an engaging position and provides an engaging configuration for rocker arm assembly 147A. If cam 127 is rotated while latch pin 133 is in the engaging position, latch pin 133 may engage lip 131 of inner arm 111A. The force of cam 127 on cam follower 119 may then cause both inner arm 111A and outer arm 111B to pivot together on hydraulic lash adjuster 165, bearing down on valve 106 and compressing valve spring 105 as shown in FIG. 3. Valve 106 may thus be lifted off its seat 102 with a valve lift profile determined by the shape of cam 127. The valve lift profile is the shape of a plot showing the height by which valve 106 is lifted off its seat 102 as a function of angular position of cam shaft 125. In the engaging configuration, cam shaft 125 may do work in engine 117 as cam 127 rises off base circle. Much of the resulting energy may be taken up by valve spring 105 and returned to cam shaft 125 as cam 127 descend back toward base circle.

(26) FIG. 4 shows the result if cam 127 is rotated while latch pin 133 is in the non-engaging position. The downward force on cam follower 119 may be distributed between valve 106 and torsion springs 159. Torsions springs 159 may be tuned relative to valve spring 105 such that torsion springs 159 yield in the non-engaging configuration while valve spring 105 does not. Inner arm 111A may descend as torsion springs 159 wind and outer arm 111B may remain in place. As a result, valve 106 may remain on its seat 102 even as cam 127 rotates. In the non-engaging configuration, cam shaft 125 still does work in engine 117 as cam 127 rises of base circle. But in this case most of the energy is taken up by torsions springs 159, which act as lost motion springs.

(27) Electromagnetic latch assembly 150A may be powered in any suitable manner. In this example, electromagnetic latch assembly 150A is powered through a spring 143 bound at one end to rocker arm 111B and at the other end to a structure mounted off rocker arm 111B, such as cam carrier 145. The bindings are made by insulated connectors 142 and 144. Connector 144 may bind one end of wire 143 to cam carrier 145, cylinder head 103, a camshaft bearing journal, or any other part that is substantially stationary relative to cylinder head 103. Spring 143 may have a natural frequency of 500 Hz or greater to dampen oscillations caused by motion of rocker arm 111B. Spring 143 is a coil or ribbon metal, although any suitable type of spring may be used. Rather than carry the current through spring 143, the vibration damping of spring 143 may still be used if the current is carried by a conductive trace on spring 143 or a wire bound to spring 143 along spring 143's length. A ground connection may be formed using a second spring, a second wire or conductive trace on spring 143, or through the structure of rocker arm assembly 147A.

(28) Solenoid 143 may be connected in a circuit 300A for which FIG. 5 provides an example. Circuit 300A includes solenoid 143, a DC power source 303, a switch 305E that selectively connects power source 303 to solenoid 143, a sensor 311 configured to measure current in circuit 300A, and a flyback diode 309. The components other than solenoid 139 may be mounted in positions that are off rocker arm assembly 147A and are stationary relative to cylinder head 103. A control signal 307E for switch 305E may be provided by a controller (not shown). The controller may be an engine control unit (ECU).

(29) FIGS. 6 and 7 illustrate an internal combustion engine 117B that may be similar in most respects to internal combustion engine 117A. Engine 117B has an electromagnetic latch assembly 150B and coils 151 and 155, which are proximate but separated by an air gap 152. Coil 151 is mounted to rocker arm 111B and is connected in series with solenoid 139. Coil 151 could alternatively be connected in parallel with solenoid 139. Coil 155 is mounted off rocker arm assembly 147B and is attached by bracket 153 to cylinder head 103. Rocker arm assembly 147B provides rocker arm 111B with a range of motion when latch pin 133 is in the engaging position as illustrated by FIGS. 6 and 7. That range of motion spans between the no-lift position illustrated by FIG. 6 where cam 127 is on base circle to the maximum lift position illustrated by FIG. 7. Coils 151 and 155 may be mutually inductively coupled throughout that range of motion, but the extent of that coupling and the size of the air gap 152 vary with motion of rocker arm 111B.

(30) Electromagnetic latch assembly 150B includes two annular permanent magnets 201A and 201B positioned within solenoid 139 with confronting polarities and with a low coercivity ferromagnetic ring 203 between them. Permanent magnets may be rigidly mounted with respect to solenoid 139 and outer arm 111B. Electromagnetic latch assembly 150B is bi-stable in that it provides both extended and retracted positions in which latch pin 133 is stable independently from solenoid 139. As a consequence, either the latched or unlatched configuration can be reliably maintained without solenoid 139 being powered. Positional stability refers to the tendency of latch pin 133 to remain in and return to a particular position. Stability is provided by restorative forces that act against small perturbations of latch pin 133 from a stable position. In accordance with some of the present teachings, stabilizing forces are provided by permanent magnets 201. Alternatively or in addition, one or more springs may be positioned to provide positional stability. Springs may also be used to bias latch pin 133 out of a stable position, which may be useful for increasing actuation speed.

(31) FIGS. 8-10 illustrate the operation of electromagnetic latch assembly 150B. FIG. 8 shows electromagnetic latch assembly 150B with latch pin 133 in the extended position. FIG. 10 shows electromagnetic latch assembly 150B with latch pin 133 in the retracted position. In FIGS. 8 and 10, solenoid 139 is de-energized. FIG. 9 illustrates latch pin 133 in a transitional state with solenoid 139 energized and driving latch pin 133.

(32) Electromagnetic latch assembly 150B may include various low coercivity ferromagnetic elements that are operative as pole pieces and positioned to form magnetic circuits for flux from permanent magnets 201. These include pieces 137 forming a shell around solenoid 139 and annular rings 211. Annular rings 211 may be shaped to mate with stepped edges of low coercivity ferromagnetic ring 135 mounted to latch pin 133. During actuation, magnetic flux may cross an air gap between one of these stepped edge and a mating ring 211, in which case the stepped edge may be operative to increase the magnetic forces through which latch pin 133 is actuated.

(33) As shown in FIGS. 8 and 10, permanent magnet 201A stabilizes latch pin 133 in both the extended and the retracted positions. As shown in FIG. 8, magnetic circuit 216A is operative to be the primary path for magnet flux from permanent magnet 201A when latch pin 133 is in the extended position, absent magnetic fields from solenoid 139 or any external source that might alter the path taken by flux from permanent magnet 201A. Perturbation of latch pin 133 from the extended position would introduce an air gap into magnetic circuit 216A, increasing its magnetic reluctance. Therefore, the magnetic field produced by permanent magnet 201A resists such perturbations.

(34) As shown in FIG. 10, magnetic circuit 214B is operative to be the primary path for magnet flux from permanent magnet 201A when latch pin 133 is in the retracted position, absent magnetic fields from solenoid 139 or any external source that might alter the path taken by flux from permanent magnet 201A. Perturbation of latch pin 133 from the retracted position would introduce an air gap into magnetic circuit 214B, increasing its magnetic reluctance. Therefore, the magnetic field produced by permanent magnet 201A resists those perturbations as well.

(35) FIGS. 8 and 10 show that permanent magnet 201B also stabilizes the position of latch pin 133 in both the extended and retracted positions. In the extended position, magnetic flux from permanent magnet 201B primarily follows circuit 214A. In the retracted position, magnetic flux from permanent magnet 201B primarily follows circuit 216B.

(36) Electromagnetic latch assembly 150B is structured to operate through a magnetic flux path-shifting mechanism. FIG. 9 illustrates this mechanism for the case in which solenoid 139 is operated to induce latch pin 133 to actuate from the extended position to the retracted position. A voltage of suitable polarity may be applied to solenoid 139 to induce magnetic flux following the circuit 218. The magnetic flux from solenoid 139 may reverse the magnetic polarity in low coercivity ferromagnetic elements forming the magnetic circuits 214A and 216A through which permanent magnets 201 stabilized latch pin 133 in the extended position. This greatly increases the reluctance of magnetic circuit 214A and 216A. Magnetic flux from permanent magnets 201 may thus be driven to shift from magnetic circuits 214A and 216A toward magnetic circuits 216B and 214B. The net magnetic forces on latch pin 133 may drive it to the retracted position shown in FIG. 18. The total air gap in the magnetic circuit 218 taken by flux from solenoid 139 may not vary significantly as latch pin 133 actuates. This feature relates to operability through a flux path-shifting mechanism.

(37) Magnetic circuits 216A and 216B are short magnetic circuits between the poles of permanent magnets 201A and 201B respectively. Magnetic circuits 216 pass through low coercivity ferromagnetic portion 135 of latch pin 133 but not around the coils of solenoid 139. These short magnetic circuits may reduce magnetic flux leakage and allow permanent magnets 201 to provide a high holding force for latch pin 133. Magnetic circuits 214, on the other hand, pass around the coils of solenoid 139. Routing these magnetic circuits around the outside of solenoid 139 may keep them from interfering with the shorter magnetic circuits. These longer, alternate magnetic circuits can allow permanent magnets 201 to contribute to stabilizing latch pin 133 in both extended and retracted positions and can assure there is a low reluctance magnetic circuit to help maintain the polarization of permanent magnets 201 regardless of whether latch pin 133 is in the extended or the retracted position.

(38) As used herein, a permanent magnet is a high coercivity ferromagnetic material with residual magnetism. A high coercivity means that the polarity of permanent magnet 201 remains unchanged through hundreds of operations through which electromagnetic latch assembly 150B is operated to switch latch pin 133 between the extended and retracted positions. Examples of high coercivity ferromagnetic materials include compositions of AlNiCo and NdFeB.

(39) While permanent magnets 201 may initially hold latch pin 133 in a first position, at some point during latch pin 133's progress toward the second position, permanent magnets 201 begin to attract latch pin 133 toward the second position. Accordingly, at some point during latch pin 133's progress, solenoid 139 may be disconnected from its power source and latch pin 133 will still complete its travel to the second position.

(40) Electromagnetic latch assembly 150A forms an air gap 140 shown in FIG. 2. Moving latch pin 133 toward the retracted position tends to reduce air gap 140, which reduces the magnetic reluctance in a path taken by flux from solenoid 139. As a consequence, energizing solenoid 139 in electromagnetic latch assembly 150A causes latch pin 133 to move toward the retracted position regardless of the direction of the current through solenoid 139 or the polarity of the resulting magnetic field. But in electromagnetic latch assembly 150B, latch pin 133 may be moved in either one direction or another depending on the polarity of the magnetic field generated by solenoid 139.

(41) FIG. 11 provides a drawing of a circuit 300B that may be used to drive solenoid 139 with a current in either a forward or a reverse direction depending on the desired polarity for the magnetic field. Circuit 300B is all of FIG. 11 except that portion identified as circuit 323. Circuit 300B includes current sensor 311, an H-bridge 317, solenoid 139, and coil 151. Coil 151 is connected in series with solenoid 139. Coil 151 is mutually inductively coupled with the coil 155 that is in circuit 323, but circuit 323 is still considered separate from circuit 300B for purposes of the present disclosure. Circuit 323 includes oscillator 321, which may be used to drive coil 155 with an AC current. Any suitable AC power source may be used. In some of these teachings, H-bridge 317 is operated to provide AC power and a distinct oscillator 321 is not required.

(42) H-bridge 317 may be controlled through signal 307A and 307B. Signal 307A closes switches 305A and 305C allowing current from voltage source 303 to ground 301 to flow through solenoid 139 in a first direction. Signal 307B closes switches 305B and 305D allowing current from voltage source 303 to ground 301 to flow through solenoid 139 in a second direction, which is the reverse of the first direction. Signals 307A and 307B may be provided by controller (not shown).

(43) Sensor 311 may be a current sensor that includes a shunt resistor 313 and a voltage measuring device 315 connected across shunt resistor 313. Sensor 311 may alternatively be a Hall effect sensor or any suitable type of current sensor. A voltage sensor may be used in place of a current sensor. Most of the examples provided herein describe measuring current, but substantially equivalent information may be obtainable from an appropriate voltage measurement.

(44) In accordance with some aspects of the present teachings, magnetic components of electromagnetic latch assembly 150 are mounted within a chamber 156 formed in outer arm 111B. The magnetic component housed in chamber 156 may include solenoid 139, permanent magnets 201, or both. In accordance with some of these teachings, chamber 156 is sealed against intrusion from metal particles that may be in oil dispersed throughout the surrounding rocker arm assembly 147.

(45) In accordance with some aspects of the present teachings, chamber 156 was designed to be a hydraulic chamber. Chamber 156 may have been adapted to house parts of electromagnetic latch assembly 150. In accordance with some of these teachings, rocker arm assembly 147 is made using rocker arms 111 put into production for use with a hydraulically actuated latch. In accordance with some of these teachings, an electric latch assembly 150 has been installed in place of a hydraulic latch. While chamber 156 is a hydraulic chamber, it need not be functionally connected to a hydraulic system. A hydraulic passage 158 may connect to chamber 156. Hydraulic passage 158 may be blocked to help seal chamber 156. In some of these teaching, hydraulic passage 158 couples with a hydraulic passage 160 formed in hydraulic lash adjuster 165.

(46) In accordance with some aspects of the present teachings, hydraulic lash adjuster 165 may have been originally designed for use with a hydraulically latching rocker arm assembly. Accordingly, a second supply port 166 may be formed in hydraulic lash adjuster 165 and communicate with a reservoir chamber 167 in hydraulic lash adjuster 165. Cylinder head 103 may not include any provision for supplying oil to second supply port 161. Reservoir chamber 167 may be isolated from any substantial flow of hydraulic fluid in cylinder head 103. Reservoir chamber 167 and hydraulic passages communicating therewith may be essentially non-functional in engine 117.

(47) FIG. 12 provides a flow chart of a method 380 of operating internal combustion engine 117B in accordance with some aspects of the present teachings. Method 380 begins with act 381, driving coil 155 with an AC current. Coil 155 may be one of a group of coils 155, each associated with a different rocker arm assembly 147B. The coils 155 may be connected in series or parallel, whereby all may be driven simultaneously. Act 381 may induce a current in circuit 300B through inductive coupling. The inductive coupling may be with coil 151. Alternatively, the coupling may be with solenoid 139, in which case coil 151 is optional.

(48) Act 383 is using sensor 311 to obtain data relating to a current or voltage induced in circuit 300B by act 381. Act 385 is analyzing the data to obtain information regarding the operation of rocker arm assembly 147B. Act 387 is reporting a result of that analysis. As shown in FIGS. 6 and 7, an air gap 152 between coils 151 and 155 varies in relation to the movement of rocker arm 111B through its range of motion. Air gap 152 may increase by a factor of two or more and in some cases by a factor of four or more over that range of motion. The degree of inductive coupling between coils 151 and 155 varies strongly in relation to the size of air gap 152. Accordingly, the magnitude of the current or voltage induced in circuit 300B may be indicative of the position of rocker arm 111B. In some alternative teachings, circuit 300B is driven and a current or voltage in a circuit comprising coil 155 is monitored and analyzed to provide diagnostic information that may be derived from rocker arm position data. Internal combustion engine 117B, circuit 300B, and method 380 may be modified accordingly.

(49) Method 380 may be applied with any suitable scheduling. In some of these teachings, driving coil 155 with AC current does not affect the position or actuation of latch pin 133, in which case the diagnostic circuit 311 may be driven continuously. In some of these teachings, method 311 is applied between periods when latch pin 133 is being actuated. In some of these teachings, method 380 can be carried out in a considerably shorter period of time than is required to actuate latch pin 133 and method 311 may be interleaved with application of voltage to coil 139 to drive actuation of latch pin 133. In some of these teachings, method 380 is applied only when cam 127 is off base circle.

(50) Coils 151 and 155 may be smaller than illustrated in FIGS. 6 and 7. In some of these teachings, one or both of these coils have a structure such as coil 250 shown in FIG. 13. Coil 250 is formed by a conductive trace 253 on a printed circuit board (PCB) 251. Coil 250 may have an air core. Coil 250 may have any suitable spiral pattern, e.g., square (as show), circular, hexagonal, or octagonal. Mutual inductance may be highest if both coils use the square pattern. A typical design may have a 10 mm outer diameter, 0.5 mm wide traces, an 0.25 mm spacing between turns, and 10 turns. Mutual inductance may be increased by using larger coil diameters, more turns, and/or a ferromagnetic core. The distance 154 (see FIG. 6) between cylinder head 103 and rocker arm 111B may be 4 mm or less. Providing coils 151 and 155 on PCBs 251 allows both to fit within that region while maintaining a minimum spacing of 1 mm or more between coils 151 and 155.

(51) FIG. 14 provides a flow chart of a method 400 of operating internal combustion engine 117 in accordance with some aspects of the present teachings. Method 400 begins with act 401, applying a voltage to solenoid 139 in an attempt to actuate latch pin 133. Applying a voltage to solenoid 139 may include generating a control signal 307 that closes a switch 305. In a period immediately preceding act 401, there may be no current through solenoid 139. Following act 401, current may begin to flow through solenoid 139.

(52) Act 403 is monitoring sensor 311 to obtain data relating to a time variation of current or voltage in a circuit 300 that comprises solenoid 139. The data may be obtained over a short period immediately following act 401 and the current or voltage that is measured may result from act 401. Shortly may be interpreted in terms of the time required for the current in circuit 301 to reach an approximately steady state value following a change in the applied voltage. A short period may be on the order of the length of time required to actuate latch pin 139. Actuation of latch pin 139 may be completed in less than about 50 milliseconds, typically within about 15 milliseconds.

(53) Act 405 is analyzing the data. A controller (not shown) with suitable programming may carry out the analysis. Act 407 is reporting a result of the analysis. The report may be sending a signal, such as illuminating a warning light. In some of these teachings, reporting 407 includes recording a diagnostic code in a data storage device. The diagnostic code may later be read by a technician.

(54) FIG. 15 provides a flow chart of a method 420 of operating internal combustion engine 117 in accordance with some aspects of the present teachings. Method 420 begins with act 421, decoupling solenoid 139 from a voltage source that was being used to drive solenoid 139. Accordingly, method 420 may be applied when solenoid 139 is in an energized state. In some of these teachings, act 421 may be an attempt to actuate latch pin 133. This may occur when method 421 is applied to an internal combustion engine 117A in which solenoid 139 is relied on to maintain one of the latched and unlatched configurations. In some others of these teachings, act 421 may follow an actuation of latch pin 133 when energy is no longer required in solenoid 139. This may occur when method 421 is applied to an internal combustion engine 117A in which latch pin 133 is stable in both extended and retracted positions. Act 421 may include opening one or more switches 305.

(55) Act 423 is monitoring current or voltage in a circuit 300 over a period shortly following act 421. The current or voltage may be monitored in a pathway between solenoid 139 and ground 301. Act 425 is analyzing the data and act 427 is reporting a result of that analysis. These actions may be comparable to acts 405 and 407.

(56) FIG. 16 provides a flow chart of a method 440 of operating internal combustion engine 117 in accordance with some aspects of the present teachings. Method 440 begins with act 441, monitoring current or voltage in circuit 300 at a time removed from any attempt to actuate latch pin 133. In some of these teachings, method 440 may be applied over a period where circuit 300 is expected to be at steady state. In some of these teachings, the steady state is an energized state with voltage applied to solenoid 139. In some of these teachings, the steady state is a grounded state with no voltage applied to solenoid 139.

(57) Act 441 is monitoring current or voltage in circuit 300 to detect current in solenoid 139. The current may be induced in solenoid 139 if latch pin 133 moves while latch pin 133, or ferromagnetic part 135 mounted thereto, is magnetized. Such a movement may be a critical shift. A critical shift may be defined as a shift from a latched state to an un-latched occurring while a cam 107 is off base circle. If solenoid 139 is in a de-energized state, any significant current or voltage reading from sensor 311 may be indicative of an induced current. If solenoid 139 is in an energized state, any significant variation in current or voltage readings from sensor 311 may be indicative of an induced current. Act 443 is reporting if an induced current in circuit 300 is detected.

(58) In some of these teachings, a magnetic field is provided in a position that is stationary with respect to rocker arm 111A and is such that the magnetic field is operative to induce a detectable current in solenoid 139 or coil 151 in conjunction with movement of rocker arm 111A through its range of motion. The magnetic field may be generated by a coil 155 mounted off rocker arm 111A of or by a permanent magnet, which may be provided for this purpose. The data obtained by method 440 may then be analyzed to provide diagnostic information relating to the motion of rocker arm 111A.

(59) FIGS. 17-19 plot examples of current variations with time that may be observed when method 400 is applied. Curve 501A, shown in FIG. 17, plots an example of an expected variation with time of current, I, in circuit 300A if solenoid 139 is driven with potential V beginning at time to in engine 117A. Curve 501B, shown in FIG. 18, plots an example of an expected time variation of current in circuit 300B if solenoid 139 is driven with potential V in engine 117B. Curve 501C, shown in FIG. 19, is for the case when solenoid 139 is driven with potential V in engine 117B.

(60) Over an initial period P.sub.A, which spans from t.sub.0 to t.sub.1, the position of latch pin 133 remains unchanged. Period P.sub.A may last until the magnetic force exerted by solenoid 139 on latch pin 133 has built up to the point where it equals the sum of the restorative forces retaining latch pin 133 in its initial position and the frictional forces resisting translation of latch pin 133. During period P.sub.A, the current may increase along the path of a curve 503A, 503B, 503C. Curves 503A, 503B, 503C represent the current versus time variations that would occur if the effective inductance, L, of circuit 300 remained at a constant value, L.sub.0.

(61) Curves 503A, 503B, 503C may follow a predetermined functional form. The functional form of may have parameters and depend on the components of circuit 300. The functional form may exhibit a monotonic increase in magnitude. The functional form may include an exponential decay toward a limit. The limit may depend only on the resistance, R, of circuit 300 and the applied voltage, V. The functional form may include a parameter depending on the inductance of circuit 300. In some of these teachings, the form is:

(62) $\begin{array}{cc}I=\frac{V}{R}\left(1-e^{-\left(t-t_0\right)R/L_0}\right)& \left(1\right)\end{array}$
where L.sub.0 is the inductance of circuit 300 at time t.sub.0. The inductance is expected to vary with the position of latch pin 133, but the position of latch pin 133 does not vary during period P.sub.A.

(63) At time t.sub.1 latch pin 133 begins to move. Latch pin 133 may continue to move over a period P.sub.B ending at a time t.sub.2 at which latch pin 133 has reached its final position. Movement of latch pin 133 causes the inductance of circuit 300 to vary. This may be manifest in a departure of the current versus time relationship 501A, 501B, 501C from the functional forms of curves 503A, 503B, 503C. The variation in inductance may be in the form of an increase or a decrease. The approach of I toward its asymptotic value may slow. In some examples, a trend of increasing current magnitude may reverse: current magnitude may decrease over a portion of period P.sub.B.

(64) After period P.sub.B, there follows a period P.sub.C, spanning from t.sub.2 to t.sub.3, over which the position of latch pin 133 may remain fixed in a new position. During period P.sub.C, the current may increase along the path of a curve 505A, 505B, 505C. Curves 505A, 505B, 505C may have the same functional form as curves 503A, 503B, 503C but with different parameters. For example:

(65) $\begin{array}{cc}I=\frac{V}{R}\left(1-e^{-\left(t-t_0^{*}\right)R/L_0^{*}}\right)& \left(2\right)\end{array}$
This formula is the same as Equation (1) except for the change in the time constant to t.sub.0* and the change in the inductance to L.sub.0*. The inductance L.sub.0* may be different from L.sub.0 due to the change in latch pin 133 from its initial position to its final position. The limit may be the same as the one approached by curves 503A, 503B, 503C but the exponential decay rate may be different due to the inductance of circuit 300 having changed.

(66) The period P.sub.C ends at t.sub.3. A sampling interval P for act 403 may include P.sub.A, P.sub.B, and P.sub.C and extend from t.sub.0 to t.sub.3. The time t.sub.3 may be selected in any suitable fashion. In one example, t.sub.3 is a fixed amount of time from the time at which voltage is applied to circuit 300. In another example, t.sub.3 is determined by the current, I, having changed by less than a predetermined amount or percentage over a preceding sampling interval of a predetermined length.

(67) Curve 501B may have a qualitative difference from curve 501A toward the end of period P.sub.B. Curve 501B may be affected by a spring or magnetic force configured to stabilize latch pin 133 in its final position. As latch pin 133 approaches its final position, this stabilizing force acts to draw latch pin 133 toward that final position. Under the influence of this force, ferromagnetic element 135 may induce a current in solenoid 139. This may be manifest by an additional inflection in curve 501B. The inflection may include a rapid increase in current magnitude followed by an abrupt reduction as latch pin 133 reaches the end of its range of motion.

(68) Curve 501C may be similar to curve 501B in many respects. But one difference is that the direction of the current is reversed. Another difference is that the inductance during period P.sub.C is greater than the inductance during P.sub.A, as opposed to vice versa. A third difference may be in the shapes of curves 501B and 501C during period P.sub.B due to the stabilizing forces on latch pin 133 not being symmetrical between the extended and retracted positions.

(69) In some aspects of the present teachings, the driving voltage for solenoid 139 may be disconnected prior to latch pin 133 reaching the end of its range of motion. The driving voltage may be disconnected after the point where a spring or magnetic force independent from solenoid 139 is sufficient to complete the movement of latch pin 133 to its final position. The final position may be an extended position as shown in FIG. 8 or a retracted position as shown in FIG. 10. In some of these teachings, the driving voltage is disconnected at a predetermined time. In some of these teaching, the driving voltage may be disconnected after detection of current induction in circuit 300B. Disconnecting the driving voltage before the motion of latch pin 133 has completed may increase the sensitivity of data obtained by sensor 311 to the behavior of latch pin 133 and thus facilitate making diagnostic determinations.

(70) In some aspects of the present teachings, an attempt is made to actuate latch pin 133 following which current versus time data over a sampling interval P is analyzed to provide an indication of whether the attempt was successful. If latch pin 133 fails to actuate, the variation of current versus time may be expected to have a form indicative of a constant inductance such as the form of curve 503 or 505. The data may be analyzed to determine whether it corresponds to the functional form of these curves or the data may be analyzed to determine if it has characteristics of a variable inductance such as a form represented by one of the curves 501A, 501B, 501C. In some of these teachings, the data is compared to functional forms or characteristics of both types of curves to provide a more reliable diagnostic determination.

(71) In some of these teachings, the data is analyzed to determine whether it conforms to a functional form expected if latch pin 133 fails to actuate. The analysis may include determining parameters that provide a best fit to the data given a predetermined functional form, such as that of Equation (1). In some of these teaching, t.sub.0 may be taken as known from the time at which current V was applied to solenoid 139. A fixed inductance, L.sub.0, that provides a best fit to the data may then be determined. In some of these teachings, both a t.sub.0 and an L.sub.0 may be determined in order to generate a best fit to the data. In some of these teachings, a report relating to whether actuation was successful may be made based on the values of the calculated parameters.

(72) In some of these teachings, an error function measuring the deviation of the data from the functional form with the fitted parameters may be calculated and the report may be made based on the magnitude of the error function. An error function may be a sum of squares of differences normalized for the number, n, of current-time data points (I.sub.i, t.sub.i). For examples, the error function may be:

(73) $\begin{array}{cc}E=\frac{1}{n}\underset{1}{\overset{n}{.Math.}}{\left(I_i-\frac{V}{R}\left(1-e^{-\left(t_i-t_0\right)R/L_0}\right)\right)}^2& \left(3\right)\end{array}$
The value of E, or a result of comparing of E with a critical value, may be reported to provide an indication of whether latch pin 133 successfully actuated. A low value of E may be indicative of latch pin 133 not having moved.

(74) In some of these teachings, the data is analyzed to determine whether it has a functional form or characteristics displayed by a curve 501A, 501B, 501C during or bordering period P.sub.B. In some of these teachings, current data is analyzed to determine if the current data displays a trend of decreasing magnitude over some portion of period P. The presence or absence of such a trend may indicate whether latch pin 133 moved. In some of these teachings, the current data is analyzed to determine whether its second derivative has characteristics of a curve 501A, 501B, 501C. For example, any of whether the second derivative's magnitude exceeds a critical maximum, falls below a critical minimum, or changes sign may provide an indication of whether actuation of latch pin 133 was successful or not.

(75) In some of these teachings, a first portion of the data may be analyzed to determine a starting inductance L.sub.0 and a second portion of the data may be analyzed to determine a finishing inductance L.sub.0*. A comparison of these two inductances may provide an indication of whether actuation was successful. In some of these teachings, the comparison may involve taking the difference between these two inductance values. In some of these teachings, the comparison may involve forming a ratio of these two inductance values. A ratio may facilitate comparison with a predetermined threshold that is constant or varies comparatively weakly with temperature or other factors.

(76) In some aspects of the present teachings, the data may be analyzed to determine whether latch pin 133 moved to a sufficient extent. In some of these teachings, the data may be analyzed to determine a time t.sub.1 at which motion of latch pin 133 begins, a time t.sub.2 at which motion of latch pin 133 ends, or both. For example, a first portion of the data may be analyzed to determine a starting inductance L.sub.0 defining a curve 503A, 503B, 503C. The time at which a curve 501A, 501B, 503C deviates from a curve 503A, 503B, 503C may provide t.sub.1. A second portion of the data may be analyzed to determine a finishing inductance L.sub.0* defining a curve 505A, 505B, 505C. The time at which a curve 501A, 501B, 501C meets a curve 505A, 505B, 505C may provide t.sub.2. The difference between t.sub.2 and t.sub.1 is the length of period P.sub.B. If period P.sub.B is below a predetermined minimum, a report may be made that latch pin 133 does not appear to have moved sufficiently. In some of these teachings, a determination of whether latch pin 133 moved may be made based on a comparison between the starting inductance L.sub.0 and the finishing inductance L.sub.0*. If the difference is not great enough, that may indicate that latch pin 133 did not move sufficiently. Other examples may include calculating the energy delivered to solenoid 139 over period P.sub.B. If, after subtracting resistive losses in circuit 300, the energy delivered to solenoid 139 is less than a predetermined amount, it may be reported that latch pin 133 does not appear to have moved sufficiently.

(77) In some aspects of the present teachings, the data is analyzed to determine whether latch pin 133 was in an expected position at the beginning of latch pin actuation. This may include analyzing data taken over an early portion of interval P to calculate a starting inductance L.sub.0. The calculated value may be compared to an expected value. In some of these teaching, an expected value may be based on calibration. In some of these teachings, an expected value may be determined from measurements taken during previous operation of latch 133. In some of these teaching, an expected value may be indexed to or made functionally dependent on temperature. If the calculated value is not reasonably close to the expected value, then the discrepancy may be reported.

(78) In some aspects of the present teachings, the data is analyzed to determine whether latch pin 133 reached an intended final position. This may include analyzing the data taken over a later portion of interval P to calculate a finishing inductance L.sub.0*. The calculated value may be compared to an expected value. If the calculated value is not reasonably close to the expected value, then the discrepancy may be reported.

(79) In some aspects of the present teachings, the data may be analyzed to determine whether latch pin 133 is sticking. Curve 515 of FIG. 17 plots an example of an expected current variation with time if latch pin 133 is sticking. Sticking may be determined from the high magnitude the current reaches before latch pin 133 begins to move. That magnitude may be compared to a predetermined value. Like other predetermined values described herein, the predetermined value may be a temperature-dependent value.

(80) Curve 501C, shown in FIG. 19, plots an example of an expected variation with time of current, I, through solenoid 139 if a potential V is applied to circuit 300B at time t.sub.0. This may be an attempt to actuate latch pin 133 from its retracted to its extended position. For an initial period P.sub.A, curve 501C is expected to follows curve 505C, which is indicative of circuit 300B having a constant inductance at a value associated latch pin 133 being in a retracted position. There may follow a period P.sub.B in which the inductance is affected by motion of latch pin 133. The inductance is affected by the changing geometry and the inductive effect of latch pin 133's motion. If actuation is successful, a period P.sub.C is reached over which curve 501C may follow curve 503C, which is indicative of circuit 300 having a constant inductance at a value associated latch pin 133 being in an extended position. The case plotted in FIG. 19 is similar to that of FIG. 18 except that the current through solenoid 139 in a reverse direction and the final inductance is less than the stating inductance.

(81) FIG. 20 plots examples of current variation with time that may be observed when method 420 is applied. In some of these teachings, latch pin 133 may be expected to actuate in response to decoupling solenoid 139 from voltage source 303. In that case, the expected variation is that of curve 507. In some of these teachings, latch pin 133 may be expected to remain in its current position when solenoid 139 is decoupled from voltage source 303. In that case, the expected variation is that of curve 509.

(82) While solenoid 139 is energized, it may generate a magnetic field in which a significant amount of energy is stored. Most of that energy may be dissipated in a period immediately following decoupling solenoid 139 from voltage source 303. One mechanism by which this energy dissipates is inducing a reverse polarity current in a circuit 300.

(83) A variation such as curve 507 may be expected for the case where latch pin 133 moves following decoupling solenoid 139 from voltage source 303 at time t.sub.4. Over an initial period P.sub.D, which extends from t.sub.4 to t.sub.5, the current through the circuit 300 may reverse direction. The reverse polarity current may reach a peak magnitude at t.sub.5, after which it may begin an exponential decay toward zero. The decay follows curve 509. Curve 509 may follow a predetermined functional form with a parameter that depends on the inductance of the circuit 300. If latch pin 133 moves, the inductance of circuit 300 is expected to vary. Curve 507 departs from curve 509 at time t.sub.6, which is when latch pin 133 begins to move. Latch pin 133 may be in motion for a period P.sub.F, which extends from t.sub.6 to t.sub.7. During a portion of period P.sub.F, the magnitude of current in circuit 300 may reverse its trend of decreasing and undergo a period of increase analogous to the behavior of curves 501A, 501B, 501C during period P.sub.B. For the period P.sub.G, extending from t.sub.7 to the end of the sampling interval at t.sub.8, curve 507 may follow a predetermined functional form having a parameter reflecting the inductance of circuit 300 when latch pin 133 is in its final position.

(84) In some of these teachings, current or voltage data is analyzed to determine the initial position of latch pin 133 at the time solenoid 139 is decoupled from voltage source 303. In some of these teachings, the position is determined from a parameter relating to inductance of circuit 300 during period P.sub.E. In some of these teachings, the position is determined from a voltage, current, or energy magnitude measured over all or part of the sampling interval. More energy may be stored in the magnetic field when latch pin 133 is in the retracted position as compared to the extended position. The energy may be estimated from an integration involving the data. The energy may also be reflected by the magnitude of a peak in a voltage or current.

(85) In some of these teaching, the force of a spring 141 is expected to move latch pin 133 from the retracted position to the extended position. The current in circuit 300 after solenoid 139 has been decoupled from a power source may be analyzed to determine whether this movement takes place. If spring 141 drives latch pin 133 toward the extended position, residual magnetism in latch pin 133, or a ferromagnetic part 135 mounted thereto, may induce a current in solenoid 139. The energy carried by the reverse current may be less than expected if latch pin 133 does not move from the retracted position to the extended position following decoupling from the power source. If analysis of the data shows the energy was significantly less than expected or otherwise shows that the reverse current is not in conformity with expectations, that information may be reported and may indicate that latch pin 133 is stuck in the retracted position.

(86) In some of these teaching, latch pin 133 has two stable positions and is expected to remain in the retracted position after solenoid 139 is decoupled from a power source. In this situation also, the current in circuit 300A may be analyzed to determine whether latch pin 133 moved.

(87) FIG. 21 provides a flow chart of a method 460 in accordance with some other aspects of the present teachings. Method 460 begins with act 461, applying a voltage pulse to circuit 300, which comprises solenoid 139. The voltage pulse may be too small in magnitude or too short in duration to affect the position of latch pin 133. Act 463 is obtaining data relating to a current of voltage variation in circuit 300 caused by the pulse. The periods of providing the pulse and collecting the data may be overlapping. Act 463 may be carried out simultaneously with act 461. In some of these teaching, the data collection period is no more than one order of magnitude greater than the period required to generate the pulse.

(88) Acts 465-469 are optional actions that will be discussed shortly. In some of these teachings, method 460 proceeds directly to act 471, analyzing the data. The current of voltage variation monitored in act 463 may exhibit a current or voltage variation having a predetermined functional form having a parameter related to the inductance in circuit 300. The inductance may vary according to the position of latch pin 133. According, the value of the parameter related to inductance may be evaluated from the data and used to provide an indication of the position of latch pin 133, which may be reported with act 473. Evaluating the parameter value may include comparing it with one or more previously determined values. A previously determined value may depend on temperature. Previously determined values may be provided for one positions of latch pin 133 or for two positions.

(89) Optionally, following act 463, an attempt is made to actuate latch pin 133. In some of these teachings, act 461 may be initiated in response to a command to actuate latch pin 133. In some of these teachings, act 461 may be allowed time to complete prior to carrying out the command. In some of these teachings, act 461 is carried out while cam 107 is off base circle.

(90) Act 467 is applying a second voltage pulse to circuit 300 and act 469 is obtaining data relating to a current of voltage variation in circuit 300 caused by that pulse. Acts 467 and 469 may follow act 465 and be timed to allow actuation of latch pin 133 to be completed before they begin. Act 467 and 469 may be repetitions of acts 461 and 463. In some of these teachings, the repetitions take place from time-to-time, without reference to the scheduling of any attempt to actuate latch pin 133.

(91) In some of these teachings where acts 467 and 469 are employed, act 471 may include comparing values of a parameter related to the inductance of circuit 300, one obtained from act 463 and the other obtained from act 469. If the values are close, that may be taken as an indication that latch pin 133 has not moved. If the values are sufficiently different, that may be taken as an indication that latch pin 133 moved between applications of the voltage pulses.

(92) In another aspects of the present teachings, a piezoelectric device is placed between latch pin 133 and a stop for latch pin 133 in either the extended or retracted position. Data from the piezoelectric device may then be used to determine whether latch pin 133 is against the stop.

(93) In another aspects of the present teachings, a circuit is formed that closes when latch pin 133 reaches an extended or retracted position. The circuit may include sliding contacts between latch pin 133 and a surrounding body. Brushes or rollers may be used in the contacts. In another aspects of the present teachings, two sets of such contact are used to form a potentiometer, which is a circuit with a length varies as latch pin 133 translates. The resistance of the circuit may then be used to determine latch pin position.

(94) The components and features of the present disclosure have been shown and/or described in terms of certain teachings 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 some aspects of the present teachings or examples, 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.