Electromechanical valve lash adjuster

Abstract

An internal combustion engine includes a cylinder head, a poppet valve having a seat within the cylinder head, a cam shaft on which is mounted an eccentrically shaped cam, and a rocker arm assembly comprising a rocker arm, a cam follower, and an electromagnetically actuated lash adjuster. The lash adjuster provides a continuously variable length fulcrum for the rocker arm. The actuator may be a piezoelectric stepper motor. The lash adjuster may be operative to vary a rate of internal exhaust gas recirculation and without requiring crank angle data.

Claims

1. An internal combustion engine, comprising: a cylinder head in which is formed a cylinder; a poppet valve for the cylinder having a seat within the cylinder head; a cam shaft on which is mounted an eccentrically shaped cam; and a rocker arm assembly comprising a cam follower and a rocker arm; and an electromechanical lash adjuster comprising an electromechanical actuator, a first end, a second end, and a length between the first end and the second end; wherein the first end provides a fulcrum for the rocker arm assembly; the second end is supported by the cylinder head; the electromechanical actuator is operative to forcibly extend the length between the first end and the second end; the cam follower is positioned to engage and follow the eccentrically shaped cam as the cam shaft rotates; and the rocker arm assembly is operative to form a first force transmission pathway through which force from the eccentrically shaped cam is transmitted to the poppet valve to actuate the poppet valve.

2. An internal combustion engine according to claim 1, wherein: the electromechanical lash adjuster comprises a first part and a second part; the electromechanical actuator is configured to rotate one of the first and second parts relative to the other about an axis; the first and second parts interface through one or more surfaces that are angled such that relative rotation between the first and second parts about the axis causes a linear displacement between the first and second parts along the axis to vary; and the electromechanical lash adjuster is operative as a linear actuator that varies the length between the first end and the second end in relation to relative rotation between the first and second parts.

3. An internal combustion engine according to claim 2, wherein the electromechanical actuator comprises an electromagnetic motor that is housed within an outer body of the electromechanical lash adjuster and has a spindle that is parallel to, but offset from, the axis.

4. An internal combustion engine according to claim 2, wherein the one or more surfaces through which the first and second parts interface are formed through helical threads on one or both of the first part and the second part.

5. An internal combustion engine according to claim 2, wherein the one or more surfaces through which the first and second parts interface between the first part and the second part are formed in part by an angled end surface of one or the other of the first part and the second part.

6. An internal combustion engine according to claim 2, wherein: the electromechanical lash adjuster further comprises a third part; the electromechanical actuator is configured to rotate the second part about the axis and relative to the first part and the third part; the second part interfaces with the third part through one or more surfaces that are angled such that relative rotation between the second part and the third part about the axis causes a linear displacement between the second part and the third part along the axis to vary; and the electromechanical lash adjuster is operative as a linear actuator that varies the length between the first end and the second end in relation to linear displacement between the first part and the third part.

7. An internal combustion engine according to claim 2, wherein: the electromechanical actuator comprises a piezoelectric element; and the electromechanical actuator is structured such that the piezoelectric element is operative to induce torque between the first part and the second part.

8. An internal combustion engine according to claim 1, wherein the electromechanical actuator is operative to vary the length between the first end and the second end through a clamp-extend-clamp-retract mechanism.

9. An internal combustion engine according to claim 1, wherein the electromechanical lash adjuster is operable over a range of extension through which it resists compression along its length primarily through friction.

10. An internal combustion engine according to claim 9, wherein the electromechanical lash adjuster is structured whereby the friction force that resists compression increases as load on the electromechanical lash adjuster increases.

11. An internal combustion engine according to claim 1, wherein: the rocker arm assembly comprises an auxiliary rocker arm; the rocker arm and the auxiliary rocker arm are pivotally linked to form a joint proximate the fulcrum; and the auxiliary rocker arm has an end distal from the joint and mounted at a position that is substantially fixed relative to the cylinder head.

12. An internal combustion engine according to claim 1, further comprising: a generator mounted to or forming a part of the electromechanical lash adjuster; wherein the electromechanical actuator is configured to be powered by energy produced by the generator.

13. An internal combustion engine according to claim 1, wherein the electromechanical actuator is housed within an outer body of the electromechanical lash adjuster.

14. An internal combustion engine according to claim 1, wherein the eccentrically shaped cam lacks a base circle structure.

15. A method of operating an internal combustion engine according to claim 1, comprising: collecting data relating to a timing with which the eccentrically shaped cam is applying a force to or inducing a displacement in the poppet valve or a component of the rocker arm assembly; and operating the electromechanical actuator to adjust lash in the first force transmission pathway on the basis of the data relating to the timing.

16. A method of operating an internal combustion engine according to claim 1 comprising: detecting force on a piezoelectric element of the electromechanical actuator to provide a force detection; and using the force detection to provide diagnostic information or feedback control; wherein the piezoelectric element is also used to effectuate lash adjustment.

17. The method of claim 16, wherein the piezoelectric element is operative to detect vibrations and the diagnostic information relates to wear.

18. An internal combustion engine, comprising: a cylinder head in which is formed a cylinder; a poppet valve for the cylinder having a seat within the cylinder head; a cam shaft on which is mounted an eccentrically shaped cam; and a rocker arm assembly comprising a cam follower and an electromechanical lash adjuster; wherein the electromechanical lash adjuster comprises a first end, a second end, a length between the first end and the second end, and an electromechanical actuator operative to forcibly increase the length between the first end and the second end; the first end provides a fulcrum for the rocker arm assembly; the second end is supported by the cylinder head; the cam follower is positioned to engage and follow the eccentrically shaped cam as the cam shaft rotates; and the rocker arm assembly is operative to form a first force transmission pathway through which force from the eccentrically shaped cam is transmitted to the poppet valve to actuate the poppet valve.

19. An internal combustion engine according to claim 18, wherein: the electromechanical lash adjuster comprises a first part and a second part; the electromechanical actuator is configured to rotate one of the first and second parts relative to the other about an axis; the first and second parts interface through one or more surfaces that are angled such that relative rotation between the first and second parts about the axis causes a linear displacement between the first and second parts along the axis to vary; and the electromechanical lash adjuster is operative as a linear actuator that varies the distance between the first end and a second end of the electromechanical lash adjuster in relation to relative rotation between the first and second parts.

20. A valvetrain for an internal combustion engine of a type that includes a cylinder head in which is formed a cylinder, a poppet valve for the cylinder having a seat within the cylinder head, the valvetrain comprising: a cam shaft on which is mounted an eccentrically shaped cam; a rocker arm assembly comprising a cam follower and a rocker arm; and an electromechanical lash adjuster having, a first end, a second end, and a length between the first end and the second end; wherein the first end provides a fulcrum for the rocker arm assembly; the second end is supported by the cylinder head; and the electromechanical lash adjuster is an electrically powered linear actuator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Spatially relative terms, such as beneath, below, lower, above, upper and the like are used in the following detailed description to describe spatial relationships as illustrated in the drawings. Those relationships are independent from the orientation of any illustrated device in actual use.

(2) FIG. 1A is a partial cutaway side view of an internal combustion engine according to some aspects of the present teachings.

(3) FIG. 1B is a perspective view of an electromechanical lash adjuster according to some aspects of the present teachings in a retracted configuration.

(4) FIG. 1C is a perspective view of the electromechanical lash adjuster of FIG. 1B in an extended configuration.

(5) FIG. 2A is a cross-sectional view of an electromechanical lash adjuster according to some aspects of the present teachings in a retracted configuration.

(6) FIG. 2B is a perspective view of the electromechanical lash adjuster of FIG. 2A.

(7) FIG. 2C is a cross-sectional view of the electromechanical lash adjuster of FIG. 2A in an extended configuration.

(8) FIG. 2D is a perspective view of the electromechanical lash adjuster of FIG. 2C.

(9) FIG. 3 is a partial cutaway side view of an internal combustion engine according to some other aspects of the present teachings.

(10) FIG. 4A is a partial cutaway side view of an internal combustion engine according to some other aspects of the present teachings.

(11) FIG. 4B is a cross-sectional view of an electromechanical lash adjuster according to some aspects of the present teachings in a retracted configuration.

(12) FIG. 4C is a perspective view of the electromechanical lash adjuster of FIG. 4B.

(13) FIG. 4D is a cross-sectional view of the electromechanical lash adjuster of FIG. 4B in an extended configuration.

(14) FIG. 4E is a perspective view of the electromechanical lash adjuster of FIG. 4D.

(15) FIG. 4F is a perspective view of an electromechanical actuator that is in accordance with some aspects of the present teachings and is used in the electromechanical lash adjuster of FIGS. 4B-4E.

(16) FIG. 5 is a flow chart of a method used in some aspects of the present teachings

(17) FIG. 6A is a perspective view of an electromechanical actuator that may be used in accordance with some aspects of the present teachings.

(18) FIG. 6B is an exploded view of the actuator of FIG. 6A.

(19) FIGS. 6C-6G are a series of drawings illustrating the operation of the actuator of FIG. 6A.

(20) FIG. 7 is a flow chart of a method according to some aspects of the present teachings.

(21) FIG. 8A is a perspective view of an electromechanical lash adjuster according to some aspects of the present teachings in a retracted configuration.

(22) FIG. 8B is a perspective view of the electromechanical lash adjuster of FIG. 8A in an extended configuration.

(23) FIG. 8C is a cross-sectional view of the electromechanical lash adjuster of FIG. 8A in a retracted configuration.

(24) FIG. 8D is the same view as FIG. 8C but with the electromechanical lash adjuster in an extended configuration.

DETAILED DESCRIPTION

(25) 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, engine 100 is the same as engine 100A, 100B, 100C, 100D. Engine 100 is therefore a generic reference that includes the specific instances engine 100A, engine 1006, etcetera. 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.

(26) FIG. 1 provides a partial cutaway side view of an internal combustion engine 100A according to some aspects of the present teachings. The view includes a portion of a cylinder head 101, a poppet valve 102 having a seat 103 within cylinder head 101, an eccentrically shaped cam 104A mounted on a cam shaft 105, and a rocker arm assembly 109A. Rocker arm assembly 109A includes a rocker arm 106A, an electromechanical lash adjuster 111A, and a cam follower 108. Cam follower 108 is mounted to rocker arm 106A and is positioned to engage and follow cam 104A as cam shaft 105 rotates. Cam follower 108 is a roller follower, although another type of cam follower such as a slider could be used instead.

(27) Rocker arm assembly 109A forms a force transmission pathway through which force from cam 104A may be transmitted to actuate poppet valve 102. Lash 107 occurs in this force transmission pathway. Lash 107 is illustrated as occurring between cam 104A and cam follower 108, but may occur elsewhere in the force transmission pathway such as between rocker arm 106A and poppet valve 102.

(28) Electromechanical lash adjuster 111A is extensible between a first end 131A and a second end 133A thereof. First end 131A provides a fulcrum on which rocker arm 106A pivots. Electromechanical lash adjuster 111A includes an electromechanical actuator 115A operable to vary the length of lash adjuster 111A, which the distance between first end 131A and second end 133A. Adjusting the length of electromechanical lash adjuster 111A varies the height of first end 131A above cylinder head 101 and thereby controls lash 107. Electromechanical actuator 115A is operable to continuously vary the length of electromechanical actuator 115A while engine 100A is operating, although lash adjustment may be prevented when cam 104A is loading rocker arm assembly 109A.

(29) Electromechanical lash adjuster 111A includes an upper part 110A and a lower part 112A. Lower part 112A is nearly cylindrical and provides an outer body for lash adjuster 111A. Electromechanical actuator 115A is housed within that outer body. In conjunction with upper part 110A, lower part 112A protects electromechanical actuator 115A from metal particles in oil that may be dispersed throughout the environment surrounding lash adjuster 111A. The metal particles might otherwise be attracted by magnetic components of electromechanical actuator 115A and interfere with its operation.

(30) FIG. 1B provides a perspective view of electromechanical lash adjuster 111A in a retracted configuration while FIG. 1C provide the same view after actuation to a more extended configuration. Upper part 110A and lower part 112A interface through helical threads 114. Threads 114 are pitched, and therefore angled, such that rotating part 110A about its axis 150 while part 112A is prevented from rotating about axis 150 results in relative rotation between these parts, causes a linear displacement between upper part 110A lower part 112A, extends or contracts lash adjuster 111A depending on the direction of relative rotation, and raises or lowers the height of fulcrum 131A over cylinder head 101 thereby adjusting lash 107.

(31) Upper part 110A may be, in part, an externally threaded shaft while lower part may be, in part, an internally threaded tube. Electromechanical lash adjuster 111A is continuously variable in length by relative rotation between upper part 110A and lower part 112A. Electromechanical actuator 115A includes an electromagnetic motor 116 that is coaxial with upper part 110B and lower part 112B. Operation of electromagnetic motor 116 may be controlled through a controller (not shown). The controller may be an engine control unit (ECU) or a separate controller associated with lash adjuster 111A

(32) FIGS. 2A-2D show a different electromechanical lash adjuster 111B that may be used in engine 100 in place of electromechanical lash adjuster 111A. Lash adjuster 111B includes an upper part 110B, a lower part 112B, and an intermediate part 131B. Intermediate part 131B has internal threads 124 formed on an inner surface 126 and external threads 123 formed on its outer surface. Internal threads 124 and external threads 123 having opposite orientations, one set being left-hand threads and the other being right-hand threads. Intermediate part 131B may be considered a tube. Internal threads 124 may engage external threads 122 of upper part 110B. External threads 123 may engage internal threads 125 of lower part 112B. These threads provided angled surfaces through which these parts interface. Relative rotation between upper part 110B and lower part 112B may be prevented by an anti-rotation guide 135B, which is mounted to lower part 112B and travels within a slot 132B in upper part 110B. Motor 116 may be housed within, and fixed to prevent rotation with respect to, lower part 112B. A shaft 121 of motor 116 may be coaxial with threads 122, 123, 124, and 125 and have a non-circular cross-section, e.g. D-shaped, that mates with an opening 120 in intermediate part 131B allowing motor 116 to drive rotation intermediate part 131B.

(33) FIGS. 2A and 2B provide cross-sectional and perspective views of lash adjuster 111B in a retracted configuration. FIGS. 2C and 2D provide corresponding views with lash adjuster 111B in a relatively more extended configuration. Motor 116 is operative to actuate lash adjuster 111B between these configurations by rotating shaft 121. The rotation of intermediate part 131B by motor 116 results in linear displacement between intermediate part 131B and each of parts 110B and 112B. Moreover, the rotation causes a linear displacement between parts 110B and 112B, which varies the length of lash adjuster 111B, which is characterized by a distance between its first end 131B and its second end 133B.

(34) Internal threads 124 and external threads 123 may have differing pitches. The ratio between rotations of shaft 121 and units of extension of lash adjuster 111B may be controlled by varying the pitch of threads 122 and 124 and/or the pitch of threads 123 and 125. For example, internal threads 124 may have a pitch of about 0.2 mm and external threads 123 may have a pitch of about 0.3 mm.

(35) FIG. 3 illustrates an engine 100C having an electromechanical lash adjuster 111C Lash adjuster 111C includes a shaft 112C and a ball 110C engaged by threads 114. Rocker arm 106C pivots on a rounded upper surface of ball 110C, which provides a fulcrum 131C for rocker arm 106C. The upper surface may be cylindrical or have another suitable shape such that engagement between ball 110C and rocker arm 106C may prevent rotation of ball 110C. Motor 116 may be mounted above rocker arm 106C in a position that is fixed with respect to cylinder head 101.

(36) If ball 110C is prevented from rotating relative to rocker arm 106C, rotation of shaft 112C by motor 116 may cause ball 110C to travel along shaft 112C, raising or lowering the fulcrum 131C for rocker arm 106C and thereby adjusting lash. Shaft 112C may pass through an opening 122 in rocker arm 106C that allows motor 116 to be mounted above rocker arm 106C. Motor 116 may be mounted to a cam carrier (not shown) or any part that is held in a fixed position relative to cylinder head 101. Shaft 112C may rest atop a load cell 113, which may provide information useful for diagnostics or control.

(37) FIG. 4A provides a partial cross-section of an engine 100D having a rocker arm assembly 109D. Rocker arm assembly 109D includes a rocker arm 106D and an electromechanical lash adjuster 111D. Lash adjuster 111D provides a fulcrum for rocker arm 106D. Lash adjuster 111D is operative as a linear actuator to vary the spacing between that fulcrum and cylinder head 101. Lash adjuster 111D includes an upper part 141 and a lower part 143, which are telescopically engaged, whereby upper part 141 can slide relative to lower part 143 making the length of lash adjuster 111D continuously variable. Upper part 141 and lower part 143 are joined by an electromechanical actuator 115D, which is a piezoelectric stepper motor operable through a clamp-extend, clamp-retract mechanism. Upper part 141 provides an outer body for lash adjuster 111D and houses electromechanical actuator 115D.

(38) Rocker arm assembly 109D further includes a pair of auxiliary rocker arms 117 flanking rocker arm 106D and pivotally connected at one end to rocker arm 106D through axle 118, which provides a joint proximate the fulcrum. The distal ends of auxiliary rocker arms 117 may be pivotally mounted on an axle 119. Axle 119 may be mounted to a cam carrier (not shown) or other position fixed relative to cylinder head 101. Auxiliary rocker arms 117 may be positioned to mitigate off axis forces that might otherwise act against lash adjuster 111D as cam 104D actuates valve 102. In this example, off axis forces are force orthogonal to the direction in which lash adjuster 111D extends to adjust lash.

(39) FIG. 4B-4E provide additional views of electromechanical lash adjuster 111D. FIGS. 4B and 4C show lash adjuster 111D in a contracted configuration whereas FIGS. 4D and 4E show it in an extended configuration. FIG. 4F provides a perspective view of actuator 115D. As shown by these figures, actuator 115D includes a first end portion 145A and a second end portion 145B joined by a variable length central portion 148. The length of central portion 148 may be controlled through a piezoelectric element 149.

(40) Each of the end portions 145 includes a resilient element 144, a mandrel element 146, and a piezoelectric element 153. Resilient element 144 may be made of metal and may include struts 152 that are configured such that biasing resilient element 144 against mandrel element 146 causes struts 152 to bear against the bore of lower part 143, increasing friction between those parts and effectively locking the position of end portion 145 within the bore of lower part 143. The biasing force may be provided by either a piezoelectric element 153 or by a mechanical force that tends to compress lash adjuster 111D. In the absence of a sufficient biasing force, resiliency causes struts 152 to pull away from firm contact with the bore of lower part 143, which may release end portion 145 from locking engagement and allowing it to slide within the bore of lower part 143.

(41) FIG. 5 provides a flow chart of a method 200 through which engine 100D may be operated. Method 200 begins with step 201, which verifies that first end portion 145A is in a locking configuration and that cam 104D is on base circle or otherwise in a position where it is not significantly loading lash adjuster 111D. Method 200 proceeds with act 202, releasing second end portion 145B from its locking configuration. This may involve changing a voltage applied to a piezoelectric element 153. Next, act 203 extends middle portion 148. This operation may involve changing a voltage applied to piezoelectric element 149. Next, act 204 transitions second end portion 145B into a locking configuration. Next, act 205 releases first end portion 145A from its locking configuration. Act 206 is the reverse of act 203 and causes middle portion 148 to return to its contracted configuration. Act 207 returns first end portion 145A to its locking configuration. These steps may be repeated to extend electromechanical lash adjuster 111D in a series of increments. The order of these steps may be changed to contract lash adjuster 111D. Adjustment may be suspended while cam 104D is loading lash adjuster 111D. When cam 104D is applying a load to lash adjuster 111D, that load may drive both first end portion 145A and second end portion 145B into their locking configurations.

(42) One or more of the piezoelectric elements of lash adjuster 111D may undergo periodic loading in conjunction with normal operation of rocker arm assembly 109D. This loading and unloading produces voltage differentials across these piezoelectric elements. The produced voltages may be detected for diagnostic or control purposes. In addition, these voltages may be tapped, whereby these piezoelectric elements are operative as generators. The electricity may be temporarily stored and subsequently used to operate lash adjuster 111D or power a controller for it.

(43) FIGS. 6A-B illustrate an electromechanical actuator 115E that may be used in place of electromechanical actuator 115A in engine 100A or in place of electromechanical actuator 115D in engine 100D. FIG. 6A provides a perspective view of actuator 115E and FIG. 6B provides an exploded view. Actuator 115E includes a housing 155. A nut 167 may be secured within an orifice 159 at one end of housing 155. Nut 167 has internal threads 169 that engage external threads 158 on shaft 157. A guide bushing 179 having a small clearance around shaft 157 may be secured at the opposite end of housing 155. At that opposite end, housing 155 may have flanges 161 through which housing 155 may be braced to a lower part 143 such as the one shown in FIG. 4A or otherwise held stationary relative to cylinder head 101. A spherical ball tip 163 or other end piece on threaded shaft 157 may provide a fulcrum for a rocker arm 106 or may be positioned to act against an upper part 141 such as the one shown in FIG. 4A that provide a fulcrum for the rocker arm 106.

(44) Four piezoelectric plates 171 are bonded to outside surfaces 173 of housing 155. Plates 171 are positioned and operative to excite motion of housing 155 in the two orthogonal planes 175 and 177. The number and structure of piezoelectric elements 171 may be varied provided the elements 171 are operative to excite motion of housing 155 in planes 175 and 177. Piezoelectric plates 171 are operated through electrodes (not shown). Piezoelectric plates 171 may be driven with a frequency suitable to induce vibration of housing 155 and nut 167 at a resonant frequency in the ultrasonic range.

(45) As shown in FIG. 6C, exciting vibration of housing 155 and nut 167 in planes 175 and 177 with the vibrations 90-degrees out of phase is operative to induce torque between nut 167 and shaft 157 and cause nut 167 to travel along shaft 157. There is a small clearance between the threads 169 of nut 167 and the threads 158 of shaft 157. The size of this clearance is exaggerated in the images of FIG. 6C. The series of images in FIG. 6C shows how the bending of plates 171 causes an area of contact between threads 169 and threads 158 to rotate about shaft 157. This causes nut 167 to orbit shaft 157 and, with friction, generates the torque. Shaft 157 may be driven either upward or downward depending on the phase relationship between the orthogonal modes of vibration. Operation of actuator 115E may be enhanced by isolating actuator 115E from oil in the environment surrounding lash adjuster 111. That isolation may be accomplished by enclosing actuator 115E within a telescopically engaged upper part 141 and a lower part 143 like actuator 115D as shown in FIG. 4A.

(46) FIG. 7 provides a flow chart of a method 220 for controlling valve timing in an engine 100 that uses an electromechanical lash adjuster 109. Method 220 may be used to set the opening time for a valve 102 that controls either an intake or an exhaust port. By applying the method 220 to a pair of valves 102 controlling intake and exhaust ports of a single cylinder, the amount of overlap between the opening periods for those valves may be set to a pre-determined value.

(47) Method 220 involves detecting the beginnings and endings of load events on a rocker arm assembly 109. The presence or absence of such a load event can be determined based on whether the load on a lash adjuster 109 exceeds a critical value. The load may be detected by a load cell 113 such as shown in FIG. 3 or by a suitably positioned piezoelectric element such as piezoelectric element 145B shown in FIG. 4A. Alternatively, the presence of a load exceeding the critical valve can be inferred from a displacement of poppet valve 102, which may be detected by any suitable sensor.

(48) Method 220 begins with acts 221 and 223, detecting the beginnings of two consecutive load events, and act 225, detecting the end of a load event. Act 227 determines the period between load events. In this example, the determination is based on the interval between the starts of the preceding two load events. Alternative methods for calculating this period include determining the interval between the ends of two consecutive load events and more complicated methods that use additional load data to make a more accurate determination. Act 229 determines the duration of the last load event. Act 231 is operating the electromechanical lash adjuster 109 to drive a ratio between the load event duration and the load event period toward a target value. Method 220 may then return to act 223 and repeat.

(49) One possible variation on method 220 is to use the time between load events in place of the load event period. The length of time between load events may be determined as the interval between the start of a load event and the end of the preceding load event. A ratio of the length of the interval between load events and the load event period is another alternative metric that may be used without changing the effect of method 220.

(50) FIG. 8A-8D illustrate an electromechanical lash adjuster 111F according to some aspects of the present teachings. Lash adjuster 111F may be used in place of lash adjuster 111A in engine 100A or in place of lash adjuster 111D in engine 100D. Referring to FIGS. 8C and 8B, lash adjuster 111F includes two parts, lower part 307 and upper part 311, that are positioned end-to-end within an outer body 301 in a configuration that permits their relative rotation about axis 150, which is through the center of lash adjuster 111F. Lower part 307 and upper part 311 interface through abutting end surfaces 319 and 315, which are angled such that relative rotation between these parts on axis 150 causes a linear displacement between them along that axis. This capability for linear displacement makes lash adjuster 111F extensible and continuously variable in length between a first end 133F and a second end 131F thereof. End 133F is adapted to fit within a bore in cylinder head 101 and end 131F is adapted to provide a fulcrum for a rocker arm 106.

(51) Lower part 307 has radial symmetry with two repeating units. Each unit provides a surface 315 that faces upper part 311, has a generally flat profile, and angles upward at a slope of 8-10 with respect to axis 150 through most of its 180 arc length. At its uppermost extent, surface 315 has a short flat region 316 out of which there is a protrusion 317 that may have a square cross-section. Protrusion 317 is shaped to ride within a channel 309 formed in upper part 311. Channel 309 has an arc length that is somewhat less than 180. Protrusion 317 is adapted to ride freely with channel 309 under relative rotation between upper part 311 and lower part 307 until protrusion 317 encounters an end surface 310 of channel 309. Protrusion 317 cooperates with channel 309 to provide rotation-limiting stops.

(52) Upper part 311 also has, for the most part, radial symmetry with two repeating units. Each unit provides a surface 321 that faces lower part 307, has a generally flat profile except for channel 309, and angles with respect to axis 150 with the same slope as surface 315 through most of surface 321's 180 arc length.

(53) The radial symmetry of upper part 311 is broken by a slot 132F formed in upper part 311. A pin 133F fits through a bore in outer body 301 and rides within slot 132F to prevent upper part 311 from rotating relative to outer body 301. Motor 116 is secured to outer body 301 so that upper part 311 does not rotate relative to motor 116.

(54) A pinion gear 303, which is an annular gear having inward facing teeth, is formed into lower part 307, whereby it is approximately the largest gear that can be fit within outer body 301. Motor 116 is positioned off axis 150 within outer body 301 so that motor 116 can directly drive a small gear 305 that meshes with pinion gear 303. Using a small number of simple parts all fitting within outer body 301, this arrangement provides a high gear ratio between motor 116 and lower part 307 the rotation of which is driven by motor 116.

(55) Lash adjuster 111F has stiffness under load. Lash adjuster 111F resists compression under load through friction. As the load of rocker arm 109 on lash adjuster 111F increases, the friction force between surfaces 315 and 319 remains larger than the torque that load introduces between parts 307 and 311 due to the angled interface between those surfaces. A slope of 10 degrees is approximately the greatest these surfaces can have without providing one or both of surfaces 315 and 319 with a high friction material such as one of the high friction material used in transmissions.

(56) In some aspects of the present teachings, in order to maintain a desired range of motion for lash adjuster 111F and to maintain its stiffness under load without requiring high friction materials, lash adjuster 111F does not have radial symmetry. In this alternative configuration, upper part 311 has a surface 321 that interfaces with part 307 and is continuously sloping with respect to axis 150 through a radial arc in the range from 225 to 360 degrees. In some of these teachings, the slope of that surface is in the range from 4 to 7 degrees.

(57) 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.