WO2019228670A1

WO2019228670A1 - Valvetrain with electromechanical latch actuator

Info

Publication number: WO2019228670A1
Application number: PCT/EP2019/025162
Authority: WO
Inventors: Andrei Dan Radulescu; Dale Arden Stretch; Andrew Lee
Original assignee: Eaton Intelligent Power Limited
Priority date: 2018-05-30
Filing date: 2019-05-30
Publication date: 2019-12-05

Abstract

A valvetrain includes a camshaft, a latch assembly, and an actuating assembly. The latch assembly includes a latch pin (112) that selectively engages two arms (101, 103) of a rocker arm assembly. The actuating assembly includes a plunger (131), an electromagnet (119) operable to move the plunger between a first position and a second position, and a mechanical interface (110) between the plunger and the latch pin. Moving the plunger to the second position while the rocker arm assembly is off lift pulls the latch pin out of engagement. The mechanical interface has compliance that allows the plunger to move to the second position while the rocker arm assembly is being lifted by a cam and the latch pin is immobile. The mechanical interface store energy and transmits force from the plunger to the latch pin to actuate the latch pin when the rocker arm descends off lift.

Description

Valvetrain With Electromechanical Latch Actuator

Field

[0001] The present teachings relate to valvetrains, particularly valvetrains providing variable valve lift (WL) or cylinder deactivation (CDA).

Background

[0002] Hydraulically actuated latches are used on some rocker arm assemblies to implement variable valve lift (WL) or cylinder deactivation (CDA). For example, some switching roller finger followers (SRFF) use hydraulically actuated latches. In these systems, pressurized oil from an oil pump may be used for latch actuation. The flow of pressurized oil may be regulated by an oil control valve (OCV) under the supervision of an engine control unit (ECU). A separate feed from the same source provides oil for hydraulic lash adjustment. In these systems, each rocker arm assembly has two hydraulic feeds, which entails a degree of complexity and equipment cost. The oil demands of these hydraulic feeds may approach the limits of existing supply systems.

Summary

[0003] The present teachings relate to a valvetrain for an internal combustion engine of a type that has a combustion chamber and a moveable valve having a seat formed in the combustion chamber. The valvetrain includes a camshaft, a latch assembly, an actuating assembly, and a rocker arm assembly. The latch assembly includes a latch pin and a spring. The rocker arm assembly includes two rocker arms selectively engaged by the latch pin and a cam follower configured to engage a cam mounted on the camshaft as the camshaft rotates. The actuating assembly is for actuating the latch pin and includes a plunger, an electromagnet operable to move the plunger between a first plunger position and a second plunger position, and a mechanical interface between the plunger and the latch pin. The electromagnet and the plunger are mounted to a part distinct from the rocker arm assembly. The mechanical interface is structured to have compliance that allows the plunger to move from the first plunger position to the second plunger position while the cam is on lift and the latch pin remains in an engaging position. The complaint mechanism stores energy that is released to drive the latch pin out of engagement if the rocker arm descends off lift while the plunger is in the second plunger position. This structure allows the electromagnet to move the plunger into the second position while the rocker arms are engaged and being lifted by the cam but delays disengagement of the latch pin until the cam comes off lift.

[0004] One of the latch pin positions may provide a configuration in which the rocker arm assembly is operative to actuate the moveable valve in response to rotation of the camshaft to produce a first valve lift profile. The other may provide a configuration in which the rocker arm assembly is operative to actuate the valve in response to rotation of the camshaft to produce a second valve lift profile, which is distinct from the first valve lift profile, or the valve is deactivated.

[0005] In some of these teachings, the mechanical interface includes a first component that is mounted to the rocker arm assembly and a second component mounted to a part distinct from the rocker arm assembly and provides an air gap between the first component and the second component at least when the plunger is in the first plunger position. In some of these teachings, the air gap is sufficiently large that the plunger can move from the first plunger position to the second plunger position without entirely closing the air gap if the rocker arms are engaged and the cam is at an apex of lift . This structure allows the plunger to move to the second position without resistance from the latch pin. The air gap may close and tension may build in the compliant portion of the mechanical interface as the cam descends off lift. As the cam reaches base circle and weight comes off the latch pin, the tension in the compliant portion of the mechanical interface may be released to actuate the latch pin.

[0006] In some of these teachings, the actuating assembly has a greater capacity to hold the plunger against counterforce from the mechanical interface when the plunger is in the second position as compared to when the plunger is in the first position. As described above, the mechanical interface may be structured to allow the plunger to move to the second position without resistance from the latch pin. The latch pin may remain in the second position as the cam descends off lift. This allows tension to build in the mechanical interface and the latch pin to be actuated as the plunger remains in the second position where it is held most strongly by the actuating assembly.

[0007] In some of these teachings, the actuating assembly provides the plunger with positional stability without electrical power both when the plunger is in the first plunger position and when the plunger is in the second plunger position. In some of these teachings, a first permanent magnet, optionally together with additional permanent magnets, provides this stability. The permanent magnets may be positioned to contribute to this positional stability in both positions. The permanent magnets may provide sufficient holding force to maintain the plunger in the second position as the mechanical interface releases stored energy to drive the latch pin out of engagement. Enabling stability of the plunger without power reduces the amount of heat produced by the electromagnet, which allows the actuating assembly to be smaller in comparison to one in which the electromagnet must be powered continuously to maintain one or the other plunger position.

[0008] In some of these teachings, the permanent magnets are mounted to components of the actuating assembly that are distinct from the plunger. In some of these teachings, the permanent magnets are held stationary with respect to the electromagnet. In some of these teaching, the permanent magnets are mounted within the electromagnet. Keeping the weight of the permanent magnets off the plunger reduces the required size of the electromagnet.

[0009] In some of these teachings, the actuating assembly forms a first magnetic circuit that is the primary path for an operative portion of the magnet flux from the first permanent magnet when the plunger is in the first plunger position. The actuating assembly forms a second magnetic circuit that is distinct from the first magnetic circuit and is the primary path for an operative portion of the magnet flux from the first permanent magnet when the plunger is in the second plunger position. The

electromagnet encircles a volume within which a portion of the plunger comprising low coercivity ferromagnetic material translates. Both the first and the second magnetic circuits include the portion of the plunger formed of low coercivity ferromagnetic material. These features relate to a compact design.

[0010] In some of these teachings, the actuating assembly comprises one or more sections of low coercivity ferromagnetic material outside the electromagnet. The second magnetic circuit passes around the electromagnet via the one or more sections of low coercivity ferromagnetic material. The first magnetic circuit does not pass around the electromagnet. The first magnetic circuit may have an exceptionally low magnetic flux leakage and provide a high holding force on the plunger.

[0011] In some of these teachings, the actuating assembly includes a second permanent magnet and a pole piece. The second permanent magnet is arranged with confronting polarity with respect to the first permanent magnet. The pole piece is in a fixed position between the first and second permanent magnets. In some of these teachings, the pole piece abuts both the first and the second permanent magnets. In some of these teachings, the pole piece has a smaller inner diameter than the first and second permanent magnets and supports the plunger. The second permanent magnet also contributes to the stability of the plunger position both when the plunger is in the first plunger position and when the plunger is in the second plunger position. The second permanent magnet may play a complimentary role to the first permanent magnet to provide a compact and efficient actuating assembly.

[0012] In some of these teachings, the mechanical interface includes a pin-in-slot joint having a curved slot. The slot may be curved in such a way that the curvature increases the force transmitted from the plunger to the latch pin when the plunger is proximate the first position at the expense of decreasing the force transmitted from the plunger to the latch pin when the plunger is proximate the second position. This structure can reduce the electromagnet size requirement when the functionality of the actuating assembly is limited by its capacity proximate one end of its stroke to a greater extent than proximate the other end of its stroke.

[0013] Some aspects of the present teachings relate to a method of operating a valvetrain that includes receiving a latch pin actuation command, predetermining a camshaft phase angle at which to power the electromagnet, the predetermined angle varying in relation to voltage of power available to the electromagnet, temperature, and engine speed. Powering the electromagnet is delayed until the camshaft is at the predetermine phase angle. In some of these teachings, the camshaft phase angle is selected based on a determination of voltage of power available to the electromagnet and a determination of temperature. In some of these teachings, the method further includes operating the valvetrain over a range of conditions under which elapsed cam cycles between powering the electromagnet and the latch pin completing actuation varies by more than one. The timing may be selected to avoid timings in which the latch pin is only partially actuated when the cam goes on lift. In some of these teachings, the camshaft phase angle is select whereby in some instances the plunger actuates while the cam is on lift and in other instances the plunger actuates while the cam is off lift. These methods can prevent a critical shift.

[0014] In some of these teachings, the mechanical interface includes a first component that is mounted to the rocker arm assembly and a second component mounted to a part distinct from the rocker arm assembly and the valvetrain further includes a sleeve bonded to a stem of the latch pin. The first component may be a lever that acts on the latch pin by engaging the sleeve. The first rocker arm or the second rocker arm may have a gothic shaped to interface with a dome of a pivot for the rocker arm assembly.

[0015] A method of assembling a valvetrain according to these teachings includes placing the rocker arm assembly on a template that interfaces with the rocker arm assembly gothic and provides a backstop at a fixed distance from the gothic. With the latch pin in first position, the sleeve is slid along the stem until one end of the lever contacts the back stop. The sleeve is then bonded to the stem. This method fixes the position of the lever relative to the gothic to a greater accuracy than would be achieved by reliance on manufacturing tolerances. This method is particularly useful in

controlling the size of an air gap between the first component and the second

component of the mechanical interface.

[0016] In some of these teachings, an interface between the sleeve and the lever restricts rotation of the sleeve and the method further includes rotating the stem in a first direction until contact between the latch pin and the second rocker arm results in a first limit of rotation, then rotating the stem in the opposite direction until contact between the latch pin and the second rocker arm results in a second limit of rotation. The stem is set to a midpoint between the two limits of rotation before bonding the sleeve to the stem. This method accurately sets the rotational position of the latch whereby a flat end of the latch pin is correctly oriented with respect to a flat surface on the second rocker arm that the flat end of the latch pin is designed to engage.

[0017] The primary purpose of this summary has been to present certain of the inventors' concepts in a simplified form to facilitate understanding of the more detailed description that follows. This summary is not a comprehensive description of every one of the inventors' concepts or every combination of the inventors' concepts that can be considered "invention". Other concepts of the inventors will be conveyed to one of ordinary skill in the art by the following detailed description together with the drawings. The specifics disclosed herein may be generalized, narrowed, and combined in various ways with the ultimate statement of what the inventors claim as their invention being reserved for the claims that follow.

Brief Description of the Drawings

[0018] Fig. 1 is a cross-sectional view of a valvetrain according to some aspects of the present teachings with an actuating plunger extended, a latch pin in engagement, and a cam on base circle.

[0019] Fig. 2 is a cross-sectional view of the valvetrain of Fig. 1 with the actuating plunger partially retracted, the latch pin in engagement, and the cam off base circle.

[0020] Fig. 3 is a cross-sectional view of the valvetrain of Fig. 1 with the actuating plunger fully retracted, the latch pin disengaged, and the cam on base circle.

[0021] Fig. 4 is a cross-sectional view of a rocker arm assembly according to some aspects of the present teachings with a latch pin in an engaging position.

[0022] Fig. 5 is a cross-sectional view of the rocker arm assembly of Fig. 4 with the latch pin in a non-engaging position.

[0023] Fig. 6 is a perspective view of the rocker arm assembly of Figs. 4 and 5. [0024] Fig. 7 is a cross-sectional view of an actuating assembly according to some aspects of the present teachings with its plunger in an extended position.

[0025] Fig. 8 is the view of Fig. 7 with the plunger in a retracted position.

[0026] Fig. 9 is a perspective view of a valvetrain according to some aspects of the present teachings.

[0027] Fig. 10 is a perspective view of an engine including the valvetrain of Fig. 9.

[0028] Fig. 1 1 is a cut away view of the rocker arm assembly of Fig. 4

[0029] Fig. 12 is a perspective view of a sleeve according to some aspects of the present teachings for use in the rocker arm assembly of Fig. 4.

[0030] Fig. 13 is a perspective view of a lever according to some aspects of the present teachings for use with the rocker arm assembly of Fig. 4.

[0031] Fig. 14 is a plot showing a variation of force as a function of stroke for a typical solenoid.

[0032] Fig. 15 is a side view of an actuating assembly and part of a mechanical interface according to some aspects of the present teachings.

[0033] Fig. 16 is an illustration of a pin-in-slot joint used in a mechanical interface in accordance with some aspects of the present teachings.

[0034] Fig. 17 is a plot showing solenoid force as a function of stroke resistance as a function of stroke for two mechanical interfaces according to the present teachings.

[0035] Fig. 18 is a plot showing the effect of actuation response speed on a relationship between latch pin position cam phase angle.

Detailed Description

[0036] Spatially relative terms, such as“below”,“above”,“left”,“right”,“clockwise”, and“counterclockwise” and the like, may be used herein to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. These spatially relative terms are intended to encompass different orientations of the apparatus in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented or provided as a mirror image and the spatially relative descriptors used herein should be interpreted accordingly. [0037] Fig. 1 illustrates a valvetrain 104 that includes a camshaft 109, a rocker arm assembly 106, an actuating assembly 1 15 and a latch assembly 122. Rocker arm assembly 106, which is further illustrated by Figs. 4-6, is a switching roller finger follower and a cylinder deactivating rocker arm including pivotally connected inner arm 101 and outer arm 103. Latch assembly 122 include latch pin 1 12 mounted to outer arm 103. Cam follower 1 1 1 , which may be a roller follower, is mounted to inner arm 101. Cam 107 on camshaft 109 is configured to engage and actuate rocker arm assembly 106 through cam follower 1 1 1 as camshaft 109 rotates.

[0038] Latch pin 1 12 selectively engages inner arm 101 and outer arm 103. If latch pin 1 12 is in the latching position, shown in Figs. 1 , 2, and 4, actuation of inner arm 101 by cam 107 causes inner arm 101 and outer arm 103 to pivot together on pivot 140, which may be a hydraulic lash adjuster. This motion will cause a valve to open and close in relation to the cam cycle. On the other hand, if latch pin 1 12 is in the non- latching position, show in Figs. 3 and 5, actuation of inner arm 101 by cam 107 causes inner arm 101 to pivot while outer arm 103 remains stationary and the valve remains closed.

[0039] Actuating assembly 1 15 includes electromagnet 1 19 and plunger 131 , together constituting a solenoid, and two cylindrical permanent magnets 120 arranged with confronting polarities and separated by a low coercivity ferromagnetic ring 121. Electromagnet 1 19 is a coil of wire wound about bobbin 1 14 and contained within a low coercivity ferromagnetic shell 1 16. The two permanent magnets 120 and ferromagnetic ring 121 are within coil 119. Ferromagnetic ring 121 has a smaller ID than permanent magnets 120 and supports plunger 131 , keeping plunger 131 from contacting permanent magnets 120.

[0040] Fig. 1 shows plunger 131 in a first position, which is an extended position, and Fig. 3 shows plunger 131 in a second position, which is a retracted position. Fig. 2 shows plunger 131 in a position that is intermediate between the first position and the second position. Permanent magnets 120 operate on plunger 131 through low coercivity ferromagnetic ferule 123. As illustrated by Fig. 7 and 8, the magnetic circuits taken by flux from permanent magnets 120 varies as plunger 131 moves between the first and second positions. In the first position, the flux from permanent magnet 120A follows magnetic circuit 128 (see Fig. 7) which includes ring 121 and ferule 123 and goes around coil 119 through shell 116. In the second position, the flux from permanent magnet 120A follows magnetic circuit 127 (see Fig. 8), which also includes ring 121 and ferule 123 but only a small portion of shell 1 16. Magnetic circuit 127 is a very tight magnetic circuit with a low flux leakage.

[0041] Electromagnet 1 19 is operable to alter magnetic polarizations in the magnetic circuits taken by flux from permanent magnets 120. Energized with current in a first direction, electromagnet 119 is operable to cause plunger 131 to translate from the first position to the second position. Once plunger 131 is in the second position, permanent magnets 120 will stably maintain plunger 131 in the second position after power to electromagnet 1 19 is cut off. Energized with current in a second direction, which is the reverse of the first, electromagnet 1 19 is operable to cause plunger 131 to translate from the second position back to the first position. Once plunger 131 is in the first position, permanent magnets 120 will stably maintain plunger 131 in the first position after power to electromagnet 1 19 is again cut off.

[0042] Referring to Fig. 1 , valvetrain 104 includes a mechanical interface 1 10 between plunger 131 and latch pin 1 12. Mechanical interface 1 10 includes pivoting lever 134, which is mounted to outer arm 103, and pivoting component 132, which is mounted on fulcrum 133. An air gap 145 is present between pivoting lever 134 and pivoting component 132 when plunger 131 is in its extended position.

[0043] With reference to Figs. 4-6, latch assembly 122 includes a spring 1 13 that biases latch pin 112 into the latching position where it engages inner arm 101 and outer arm 103. Lever 134, which is mounted on a pin 152, acts on latch pin 1 12 via a sleeve 153 on latch pin 1 12. Driving lever 134 to pivot about pin 152 may draw latch pin 112 out of engagement as shown in Fig. 5. If pressure is release from lever 134, spring 1 13 is operative to drive latch pin 1 12 back into the engaging position as shown in Fig. 4.

[0044] Components of actuating assembly 115 including bobbin 1 14 and fulcrum 133 may be mounted to a framework 108. A stud 146 extending from a bolt 143 that secures cam cap 142 may provide a point of attachment for framework 108. Stud 146 may fit through a slot (not shown) in framework 108 and be secured by a nut 144. This structure allowing framework 108 to be slid left or right before being secured in order to set gap 145 at a desired width.

[0045] Pivoting component 132 may include a first arm 135 and a second arm 136, both of which are mounted on fulcrum 133. A spring biases first arm 135 and second arm 136 into relative rotation about fulcrum 133 up to a limit set by a stop. Plunger 131 may interface with pivoting component 132 through a pin-in-slot joint that includes pin 1 18 attached to plunger 131 and slot 141 formed in second arm 136. The pin-in-slot joint adds a degree of freedom to mechanical interface 1 10. According to some aspects of the present teachings, providing plunger 131 is a rigid component connecting with the pin-in-slot joint. This increases the rigidity of mechanical interface 1 10.

[0046] Fig. 2 shows that as plunger 131 is drawn upward by electromagnet 119 to narrow air gap 130 at the upper end of plunger 131 , pin 1 18 slides across slot 141 and drives second arm 136 upward. Driving second arm 136 upward drives first arm 135 downward in a clockwise rotation about fulcrum 133. This motion narrows air gap 145. Fig. 2 also shows the effect of cam 107 rising off base circle with latch pin 1 12 in the engaging position. Rocker arm assembly 106 pivots to the left on pivot 140, which motion increases air gap 145. The net result of these two effects is that air gap 145 is similar in size in Fig. 2 as compared to its size in Fig. 1.

[0047] Fig. 3 shows the effect of plunger 131 being drawn fully upward to close air gap 130 as cam 107 descends to base circle. The result is that air gap 145 closes completely and first arm 135 exerts force on one end of pivoting lever 134 pushing it to rotate about pin 152 causing a second end of pivoting lever 134 to pull latch pin 112 out of engagement.

[0048] Mechanical interface 1 10 has compliance. This compliance allows plunger 131 to complete its upward motion after air gap 145 has closed even if first arm 135 is unable to displace pivoting lever 134. This may occur if air gap 145 closes before cam 107 has dropped to base circle. In such case, first arm 135 and second arm 136 undergo relative rotation against the resistance of spring 137. When cam 107 drops to base circle and latch pin 1 12 becomes free to move, spring 137 may reverse the rotation, releasing stored energy, driving first arm 135 against pivoting lever 134, and pulling latch pin 112 out of engagement. Permanent magnets 120 may hold plunger 131 stationary against counterforce from mechanical interface 1 10 as this process unfolds.

[0049] Mechanical interface 1 10 provides the compliance for this process through component 132 having two independently rotating arms 135 and 136 biased against relative rotation by spring 137. The compliance may alternatively be provided by another mechanisms. One alternative mechanism is to replace pivoting component 132 by a single resilient component. Another alternative mechanism is a spring in the connection between plunger 131 and pivoting component 132, although having a rigid connection between plunger 131 and pivoting component 132 provides stiffness.

[0050] Fig. 9 provides a perspective view of valvetrain 104. As shown by this illustration, a single arm 135 of pivoting component 132 may act on two levers 134 on two adjacent rocker arm assemblies 106. In this configuration, actuating assembly 1 15 may control the actuation of two valves 105. If spring 137 and lever 136 are replaced by two springs and two levers, one actuating assembly 115 may control latching of two valves 105 having different timings.

[0051] Fig. 10 illustrates the valvetrain 104 installed in an internal combustion engine 100 having a cylinder head 102. As shown by this example, framework 108 may be mounted to two studs 146 associated with two cam caps 142 (camshaft journals).

Alternatively, framework 108 could be mounted directly to cylinder head 102, to a cam carrier, or to any other part that is itself attached to cylinder head 102. Fig. 10 also illustrates that engine 100 may have one actuating assembly 1 15 for a set of intake valves 105 and another actuating assembly 1 15 for a set of exhaust valves 105.

[0052] Air gap 145 is preferably between 0.01 mm 1.5 mm in a default configuration, which is the configuration where plunger 131 is in the lower (extended) position, latch pin 1 12 is in the engaging position, and cam 107 is on base circle. Some spacing is desirable to maintain clearance between lever 134 when latch pin 1 12 is engaged and outer arm 103 is pivoting along with inner arm 101 under the influence of cam 107. Too large an air gap may excessively increase the required stroke of plunger 131. A preferred size of air gap 145 in the default configuration is about 0.5 mm.

[0053] Fig. 1 1 illustrates a distance 160 that in part determines the size of air gap 145. Distance 160 is the distance from a position 161 that characterizes a location where rocker arm assembly 106 rests on pivot 140 to a position 162 that is a short distance 163 from pivoting lever 134. Distance 160 may be controlled and

manufacturing tolerances relaxed through the use of sleeve 153, which is illustrated in Fig. 12. During assembly, sleeve 153 may be slid along a shaft 166 of latch pin 1 12 while latch pin 1 12 in the engaging position. When sleeve 153 is at a position that sets distance 160 at the desired value, sleeve 153 may be bonded to shaft 166. The bonding process may be laser welding, or any other suitable bonding process. The bonding process may produce a permanent bond. A final adjustment determining the size of gap 145 may be made by adjusting the position of framework 108 before securing it in place.

[0054] Adjusting sleeve 153 to the desired position may be simplified through use of a template (not shown) that supports rocker arm assembly 106. The template may support rocker arm assembly 106 by gothic 165 and another point, such as elephant’s foot 164 or the like. Elephant’s foot 164 is a part of rocker arm assembly 106 designed to interface with the stem of a valve 105. The support under gothic 165 may have a shape corresponding to the dome of pivot 140. The template may include a wall or other marker at position 162, which is distance 160 from the support position 161.

Sleeve 153 may be slid along shaft 166 until distance 162 reaches a desired value. The desired value for distance 162 may be zero, in which case sleeve 153 may be slid along shaft 166 until lever 134 contact the wall or other marker at position 162.

[0055] Latch pin 1 12 may have a lip 168 with a flat surface that interface with a part 167 of inner arm 101 that also has a flat surface. The orientation of latch pin 1 12 determines whether these flat surfaces meet across a broad interface. As illustrated by Figs. 12 and 13, sleeve 153 and lever 134 may be structured to fix the orientation of latch pin 1 12. In this example, sleeve 169 has flat sidewalls that narrowly fit within an opening 170 in lever 134 having vertical sidewalls 177. When lever 134 is mounted on pin 152, sleeve 153 is fit through opening 170 and sleeve 153 is bonded to shaft 166, latch pin 1 12 is prevented from rotating.

[0056] During assembly of rocker arm assembly 106, shaft 166 may be rotated within sleeve 153 to fix latch pin 112 at the desired orientation. A method of

determining the desired orientation includes rotating shaft 166 in a first direction until contact between lip 168 and part 167 results in a first limit of rotation, then rotating the shaft 166 in the opposite direction until contact between lip 168 and part 167 results in a second limit of rotation. The midpoint between the two limits is the desired orientation of shaft 166. The desired orientation may be determined and shaft 166 set to that desired rotation prior to bonding sleeve 153 to shaft 166.

[0057] While actuating assembly 1 15 has been described as a bi-stable device, there are some instances in which the simplicity of a conventional solenoid outweighs the advantages of a bi-stable actuator. Accordingly, in some embodiments actuating assembly 1 15 is a solenoid including a spring. In the unpowered state, the spring drives plunger 131 to the extended position shown in Fig. 1 , which maximizes air gap 130. In the powered state, plunger 131 is drawn into the retracted position shown in Fig. 3, which minimizes air gap 130.

[0058] Fig. 14 provides a plot that illustrates a variation in force exerted by a typical solenoid in relation to movement of plunger 131 and corresponding variation in the size of air gap 130. The force applied by the solenoid is highest when plunger 131 is fully retracted. Accordingly, in some embodiments plunger 131 is actuated while cam 107 is on lift and air gap 145 is largest. This minimizes the resistance that plunger 131 encounters while undergoing its upward stroke. The highest holding force is required when cam 107 descends to base circle, which may occur after plunger 131 has completed its stroke. Plunger 131 may be held in its fully retracted position as air gap 145 closes and spring 137 winds. Plunger 131 may remain in its fully retracted position as spring 137 unwinds, actuating latch pin 1 12. This design may minimize a coil size and power requirement for actuating assembly 1 15.

[0059] Fig. 14 also demonstrates the importance of designing mechanical interface 1 10 to limit the required stroke for plunger 131. In some of the these teachings, plunger 131 has a stroke of 3 mm or less. The mechanical interface 1 10 of Fig. 1 allows plunger 131 to have a stroke of only about 2 mm, which is more preferable.

[0060] Fig. 15 provides another view of actuating assembly 1 15 and a portion of mechanical interface 1 10 including the pin-in-slot joint between plunger 131 and second arm 136. The pin-in-slot joint, which is further illustrated in Fig 16, includes pin 1 18 attached to plunger 131 and slot 141 formed in second arm 136. As shown by these illustrations, slot 141 curves along its length.

[0061] Fig. 17 illustrates the benefit of using the curved slot for a case in which plunger 131 is actuated to disengage latch pin 1 12 while cam 107 is off lift. Curve 171 plots the force exerted by plunger 131 as a function of stroke. Curve 172 illustrates the resistance encountered by plunger 131 if slot 141 is made straight. Over region 173 of curve 172, air gap 145 is still open and resistance is low. Resistance increase sharply and then rises linearly over region 174 over which latch pin 1 12 is actuating and spring 1 13 is compressing. Resistance undergoes another sharp increase and continues to rise linearly over region 175, over which latch pin 112 has reached the limit of its travel and further motion of plunger 131 is accommodated by winding of spring 137 in mechanical interface 1 10. As shown by this plot, if slot 141 is straight a solenoid that is more than sufficient for the requirements of region 175 is barely sufficient at the beginning of region 174 when latch pin 1 12 is beginning actuation.

[0062] Curve 176 illustrates the improvement that results from making slot 141 curved as shown in Fig. 16. The gap between available force and required force is increased at the beginning of the stroke and decreased at the end of the stroke. The net effect is a better matching of the available force to the required force across the range of the stroke, which allows the use of a smaller coil in actuating assembly 1 15. The exact curvature that balances the force requirements can vary according to the design of actuating assembly 1 15. In some instances, the force versus stroke variation may be comparatively linear and a curvature of slot 141 opposite the one shown in Fig. 16 may improve the match and reduce the coil size requirement.

[0063] A certain amount of time elapses between a coil such as electromagnet 1 19 being connected to a power source and the coil reaching sufficient power to begin moving plunger 131 and then latch pin 1 12. After plunger 131 begins movement for it and latch pin 1 12 to complete their movements. The elapsed time may be comparable to a period of rotation of camshaft 109.

[0064] In a standard vehicle electrical system, the available voltage may vary between 9 volts and 16 volts. The temperature at which actuating assembly 1 15 operates may vary over a broad range, for example from -10 °C to 150 °C. Voltage and temperature variations over these ranges can have significant effects on electromagnet power, which can in turn affect the elapsed time between powering actuating assembly 1 15 and completing actuation of latch pin 1 12. Elapsed time increases with decreasing voltage and with increasing temperature. These variations may be nearly linear. The effect of temperature on friction may add an additional level of complexity.

[0065] Fig 18 illustrates the potential effect of these variations for engine 100 running at 4000 RPM. The plot is based on actuation being initiated by powering actuating assembly 1 15 at a midpoint between two lifts of cam 107. The upper curve 181 shows the lift position of cam 107 as a function of elapsed time from initiation. The lift position of cam 107 related to the phase angle of cam 107. Curve 182 is for a high- power moderate-temperature situation. Movement of plunger 131 begins during the first lift cycle following initiation. Actuation of latch pin 1 12 completes as cam 107 comes off the first lift following initiation. Curve 184 is for a low-power high-temperature situation. Movement of plunger 131 begins during the second lift cycle following initiation.

Actuation of latch pin 1 12 completes as cam 107 comes off the second lift following initiation.

[0066] Curve 183 illustrates an intermediate condition where movement of plunger 131 begins while cam 107 is off lift. Latch pin 1 12 is partially actuated at the beginning of the second lift cycle. Partial actuation of latch pin 1 12 at the beginning of a lift cycle can result in a critical shift. A critical shift is a condition in which latch pin 1 12 slips out of engagement while cam 107 is on lift. During a critical shift, outer arm 103 may be thrust rapidly upward and a corresponding valve 105 may rapidly closed under the influence of a valve spring. Overly frequent critical shifts may result in premature wear of components in valvetrain 104. [0067] In accordance with some aspects of the present teachings, a controller (not show) avoids conditions in which latch pin 1 12 is partially actuated as cam 107 goes on lift by varying the timing of initiation. According to this teaching, the time of initiation is selected in relation to the phase of cam 107. The timing varies as voltage varies and as temperature varies. In some embodiments, a determination of timing is made on the basis of voltage and temperature. Temperature may be estimated based on an oil temperature. If an on-board diagnostic system provides feedback on the position of latch pin 1 12, timing may be determined on the basis of a recent measure of the time that elapses between initiation of actuation and the completion of travel for latch pin 1 12. The timing determination may result in an advancement or a retardation of the initiation timing used for conditions corresponding to curve 183 in comparison to the timing used for conditions corresponding to curve 182 or curve 184.

[0068] The selection of cam phase for initiation may provide a choice between plunger 131 actuating while cam 107 is on lift or off lift. In particular, both options may be available when the elapsed time between initiation and completion is short. In such situation there may be a preference for causing actuation while cam 107 to eliminate any possibility of latch pin 1 12 being pulled out of engagement prematurely.

[0069] The components and features of the present disclosure have been shown and/or described in terms of certain embodiments 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.

Claims

The claims are:

1. A valvetrain for an internal combustion engine of a type that has a combustion chamber and a moveable valve having a seat formed in the combustion chamber, comprising:

a camshaft;

a rocker arm assembly comprising a first rocker arm, a second rocker arm, a latch pin, and a cam follower configured to engage a cam mounted on the camshaft as the camshaft rotates; and

an actuating assembly for the latch pin comprising a plunger, an electromagnet operable to move the plunger between a first plunger position and a second plunger position, and a mechanical interface between the plunger and the latch pin;

wherein the latch pin is moveable between a first position in which the latch pin engages the first rocker arm with the second rocker arm as the cam lifts the first rocker arm and a second position in which the latch pin does not engage the second rocker arm as the cam lifts the first rocker arm; and

the mechanical interface is structured to provide compliance allowing the plunger to move from the first plunger position to the second plunger position while the cam is on lift and the latch pin remains in the first position and to drive the latch pin into the second position if the cam descends off lift while the plunger is in the second plunger position.

2. A valvetrain according to claim 1 , wherein the actuating assembly has a capacity to exert force on the plunger that is greater when the plunger is in the second position as compared to when the plunger is in the first position.

3. A valvetrain according to claim 1 , wherein:

the mechanical interface comprises a first component that is mounted to the rocker arm assembly and a second component mounted to a part distinct from the rocker arm assembly; and the mechanical interface provides an air gap between the first component and the second component when the plunger is in the first plunger position.

4. A valvetrain according to claim 3, wherein the air gap is sufficiently large that the plunger can move from the first plunger position to the second plunger position without entirely closing the air gap if the latch pin is engaged and the cam is at an apex of lift.

5. A valvetrain according to claim 1 , wherein:

the mechanical interface comprises a pin-in-slot joint; and

the slot of the pin-in-slot joint is curved.

6. A valvetrain according to claim 5, wherein the curvature of the slot is operative to increase the force transmitted from the plunger to the latch pin when the plunger is proximate the first position at the expense of decreasing the force transmitted from the plunger to the latch pin when the plunger is proximate the second position.

7. A valvetrain according to any one of the preceding claims, further comprising:

a sleeve bonded to a stem of the latch pin;

wherein the first component is a lever that acts on the latch pin by engaging the sleeve; and

the first rocker arm or the second rocker arm has a gothic shaped to interface with a dome of a pivot for the rocker arm assembly

8. A valvetrain according to any one of the preceding claims, wherein the actuating assembly further comprises a permanent magnet that provides the plunger with positional stability when the electromagnet is without power both when the plunger is in the first plunger position and when the plunger is in the second plunger position.

9. The valvetrain of claim 8, wherein the permanent magnet is held stationary with respect to the electromagnet.

10. A method of operating a valvetrain according to any one of the preceding claims, comprising:

receiving a latch pin actuation command;

predetermining a camshaft phase angle at which to power the electromagnet in a manner that varies in relation to voltage of power available to the electromagnet, temperature, and engine speed; and

powering the electromagnet when the camshaft is at the predetermine phase angle.

1 1. A method according to claim 10, wherein the camshaft phase angle is selected based on a determination of voltage of power available to the electromagnet and a determination of temperature.

12. A method according to claim 10, further comprising:

operating the valvetrain over a range of conditions under which elapsed cam cycles between powering the electromagnet and the latch pin completing actuation varies by more than one;

wherein the timing is selected to avoid timings in which the latch pin is only partially actuated when the cam goes on lift.

13. A method according to claim 10, wherein the camshaft phase angle is select whereby in some instances the plunger actuates while the cam is on lift and in other instances the plunger actuates while the cam is off lift.

14. A method of assembling a valvetrain according to claim 7, comprising: placing the rocker arm assembly on a template that interfaces with the gothic and provides a marker at a fixed distance from the gothic; with the latch pin in first position sliding the sleeve along the stem until one end of the lever is at a predetermined distance from the marker; and

bonding the sleeve to the stem.

15. A method according to claim 14, further comprising:

rotating the stem in a first direction until contact between the latch pin and the second rocker arm results in a first limit of rotation;

rotating the stem in a direction opposite the first until contact between the latch pin and the second rocker arm results in a second limit of rotation; and

rotating the stem to a midpoint between the two limits of rotation prior to bonding the sleeve to the stem with the stem rotated to that position;

wherein the sleeve is restricted from rotating.