Two-stage valve closure rocker assembly

Abstract

The valve actuation system includes a rocker for imparting motion to an engine valve, a motion source arranged to impart motion to the rocker, a rocker stop assembly configured to operate in an active mode in which the rocker stop assembly maintains the rocker in a position corresponding to a partial valve lift and an inactive mode in which the rocker stop assembly allows the rocker to move to a position corresponding to a fully closed valve position, and a rocker stop reset assembly for resetting the rocker stop assembly to the inactive mode following a primary event peak lift, thereby achieving delayed valve closure. A damper assembly may interact with the rocker stop assembly to provide a smooth transition of the rocker and valve motion to the delayed intake valve closing dwell. A valve catch assembly may control the seating velocity of the at least one valve.

Description

[Technical Field]

[0001] This disclosure relates to internal combustion engine valve actuation systems, including systems that provide late intake valve closing (LIVC). This disclosure also relates to valve closing timing systems and valve catch systems. This disclosure further relates to methods associated with such systems.

[0002] Engine valve actuation systems that provide LIVC in internal combustion engines are known to provide improved fuel economy and lower operating costs by varying the engine's effective compression ratio based on operating conditions. LIVC has been shown to provide slight improvements in fuel economy under certain operating conditions.

[0003] Such a system may also be advantageous by providing thermal management in engine aftertreatment systems by varying the effective compression ratio of the engine based on different operating conditions. LIVC has been shown to increase temperatures based on operating conditions. [Background technology]

[0004] There are lost motion LIVC systems that use a lost motion piston that drops within a rocker arm. However, one limitation with such systems is that the peak main event intake valve lift must be modified, which can affect performance under any operating condition (LIVC enabled vs. LIVC disabled). Therefore, it would be advantageous to provide a lost motion LIVC system that does not require modification of the peak intake valve main event lift.

[0005] Many known variable valve actuation (VVA) systems are designed to achieve the LIVC Miller cycle. For example, lost-motion VVA systems are known in which a single motion source (VVA cam profile) is configured for LIVC. In this case, the single motion source must add lift to the closing portion of the normal cam profile to achieve LIVC, and then cancel (or lose) this LIVC lift to provide normal closing timing (i.e., closing without LIVC operation). Examples of such systems can be found in U.S. Pat. No. 6,883,492 (master-slave piston arrangement in an overhead housing), U.S. Pat. No. 7,484,483 (master-slave piston arrangement in a tappet between a rocker and a valve bridge), U.S. Pat. No. 5,829,397 (master-slave piston arrangement in a tappet between a push tube and a rocker), U.S. Pat. No. 7,905,208 (dropped valve bridge), and U.S. Pat. No. 6,510,824 (dropped rocker pivot). However, such systems can have drawbacks regarding performance and cold start-up. Furthermore, the cost and complexity of such systems often make their use impractical or expensive. Therefore, it would be advantageous to provide a LIVC system that is less expensive and complex than prior art VVA systems.

[0006] Some static power systems use a fixed Miller cycle because they spend a high percentage of their time in certain operating conditions where Miller timing is desired. However, such systems do not have the ability to switch between LIVC and normal closing timing, which impacts performance in certain operating conditions.

[0007] U.S. Patent Application Publication No. 20030213443 (FIG. 1) discloses a system with a separate overhead housing designed to hold the intake rocker in the open position, thereby achieving the LIVC Miller cycle. However, the use of an electronically controlled high-speed solenoid valve disclosed therein makes the system expensive, and failure of the software or the high-speed solenoid valve can lead to valve-to-piston contact and engine damage. Therefore, a LIVC solution based on a mechanical reset system would increase reliability, reduce the risk of valve-to-piston contact, and reduce costs.

[0008] U.S. Patent No. 7,156,062 (FIG. 2) describes a system with an intermediate lost motion actuator and a self-adjusting valve catch (SAVC) that acts on a valve train element (e.g., a rocker arm) independently of the lost motion system. U.S. Patent No. 8,453,613 (FIG. 3) describes a system with an improved SAVC that acts on a valve train element independently of the lost motion system. Summary of the Invention

[0009] This disclosure describes embodiments of valve actuation systems, which may include LIVC systems, that overcome many, if not all, of the above-mentioned drawbacks of prior art systems. In lost motion LIVC systems, as described above, peak main event lift is often modified. In auxiliary rocker-based LIVC systems (e.g., U.S. Pat. Nos. 7,392,772 and 11,131,222), separate cam lobes are required, and there is a transition that must be managed between the main event and auxiliary LIVC event. One advantage of the embodiments described in this disclosure is that all lift associated with intake valve movement, including LIVC capability, can be derived from a single cam lobe. Therefore, the need for separate cam lobes and transitions of the prior art is eliminated.

[0010] To achieve LIVC, embodiments of the present disclosure may provide a valve actuation system that utilizes a rocker stop to hold the intake rocker arm position following peak main event lift, holding the valve open (typically between 3 mm and full valve lift) to achieve a later closing event. This disclosure also describes different systems and methods used to achieve a predetermined intake valve closing crank angle timing, such as hydraulic reset. Additionally, different systems and methods for controlling seating velocity by using a valve catch or sub-base circle cam closing ramp are disclosed herein.

[0011] The rocker stop in the disclosed embodiment is a hydraulic actuator piston that holds the rocker and valve open for a specific period of crank angle before a closing event occurs. In one embodiment, the rocker stop actuator piston can be positioned within the rocker arm and arranged to cooperate with a damper assembly deployed within a stationary portion of the overhead, such as the rocker shaft seat. The use of a damper ensures a smooth transition to the LIVC dwell. In an alternative embodiment, the rocker stop actuator piston can be positioned within a stationary housing to contact the valve side or cam side of the rocker arm.

[0012] The rocker arm, and therefore the valve closing timing, may in this case be controlled based on a separate system. For example, as discussed above and in accordance with prior art teachings, this may be done using an electronically controlled high-speed solenoid valve. However, in accordance with the present disclosure, a crank-angle-based reset mechanism may provide a predetermined intake valve closing timing by releasing hydraulic fluid from a high-pressure volume that otherwise maintains the actuator piston in a constant extended position (thereby holding the rocker arm / valve in an open position).

[0013] In various embodiments, the reset is triggered by the relative position of the cam with respect to the rocker arm. A rocker stop actuator piston holds the rocker stationary, so that as the cam approaches its normally closed position, it is still moving away from the rocker. A reset mechanism between the rocker and cam (or a pushrod connected to the cam) can be used to time the reset of the actuator piston relative to the crank angle to allow the rocker arm and valve to fully close.

[0014] In one embodiment, the valve seating velocity after the stalled actuator piston is reset is controlled by a valve catch (similar in structure to a damper). The valve catch may be activated only in LIVC mode by selectively switching oil supply to the valve catch. In this embodiment, the valve catch may be disposed in a stationary portion of the engine overhead environment and configured to engage the rocker arm to control shock loads and valve train dynamics. In another embodiment, a sub-base cam profile is provided with a closing ramp, and the reset mechanism allows the actuator piston to fall at a velocity such that the rocker arm follows the sub-base closing ramp.

[0015] According to one aspect of the disclosure, a valve actuation system for actuating at least one engine valve may include: a rocker for imparting motion to the at least one valve; a motion source arranged to impart motion to the rocker, the motion source defining a main event peak lift for the at least one engine valve; a rocker stop assembly configured to operate in an active mode in which the rocker stop assembly maintains the rocker in a position corresponding to a partial valve lift and a non-active mode in which the rocker stop assembly allows the rocker to move to a position corresponding to a fully closed valve position; and a rocker stop reset assembly for resetting the rocker stop assembly to the non-active mode following the main event peak lift, thereby achieving delayed valve closure.

[0016] According to further aspects of the present disclosure, a rocker stop assembly may be disposed within the rocker or elsewhere in the valve train. The rocker stop assembly may be disposed on the cam side of the rocker. The rocker stop assembly may include a hydraulically actuated piston.

[0017] According to a further aspect, the rocker stop reset assembly may be adapted to reset the rocker stop assembly to a non-operating mode at a predetermined rotational angle of the engine crankshaft or cam. The rocker stop reset assembly may include a plunger adapted to extend to occupy lash between the motion source and the rocker, the plunger further adapted to reset the rocker stop assembly to a non-operating mode when the plunger extends to the reset position. The rocker stop reset assembly may be adapted to hold the rocker stop assembly in an operating mode during a portion of a closure profile of the motion source. According to a further aspect, the motion source may be a single cam lobe.

[0018] According to a further aspect, the valve actuation system may include a damper assembly disposed in interaction with the rocker stop assembly and adapted to provide a smooth transition of the rocker and valve motion to the delayed intake valve closing dwell. The damper assembly may be disposed within a housing fixed relative to the rocker.

[0019] According to a further aspect, the rocker stop assembly and the rocker stop reset assembly may be disposed on a cam side of the rocker. The rocker stop assembly and the rocker stop reset assembly may be coupled through at least one hydraulic passage.

[0020] According to a further aspect, the motion source may include a sub-base circle cam profile having a closure ramp, and the rocker stop reset mechanism is adapted to allow the rocker stop assembly to drop at a rate such that the rocker arm follows the sub-base circle closure ramp. The rocker stop reset mechanism may be adapted to reset the rocker stop assembly to the inactive mode based on lift of the motion source and to drop at a rate independent of the motion source. The rocker stop reset mechanism may include a spring-loaded reset piston adapted to retain hydraulic fluid within the rocker stop assembly in the active mode and to vent hydraulic fluid from the rocker stop assembly to the surroundings in the inactive mode, the reset piston adapted to remain open while the rocker stop assembly is dropped.

[0021] Other aspects and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description, and the above aspects should not be considered exhaustive or limiting. The above general description and the following detailed description are intended to provide examples of inventive aspects of the present disclosure and should not be construed in any way as limiting or restrictive of the scope defined by the appended claims. [Brief explanation of the drawings]

[0022] The features described in the present disclosure are set forth with particularity in the appended claims. These features and attendant advantages will become apparent from a consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which: One or more embodiments are now described, by way of example only, with reference to the accompanying drawings in which like reference numerals represent like elements and in which: [Figure 1] 1 illustrates a prior art valve actuation system as described in the aforementioned U.S. Patent Application Publication No. 20030213443. [Figure 2] 1 illustrates a prior art valve actuation system as described in the aforementioned U.S. Pat. No. 7,156,062. [Figure 3] 1 illustrates a prior art valve actuation system as described in the aforementioned U.S. Pat. No. 8,453,613. [Figure 4] FIG. 1 is a schematic diagram illustrating exemplary high-level components and sub-components of a valve actuation system according to aspects of the present disclosure. [Figure 5] FIG. 1 is a side perspective view of a valve actuation system according to aspects of the present disclosure. [Figure 6] FIG. 1 is a top front perspective view of a valve actuation system according to aspects of the present disclosure. [Figure 7] FIG. 1 is a cross-sectional view (in a plane perpendicular to the rocker arm pivot plane) of an exemplary valve actuation system including a rocker stop assembly and a rocker stop reset assembly disposed on the motion source side of the rocker arm, and a damper assembly disposed within a stationary housing, all in accordance with aspects of the present disclosure. [Figure 8] FIG. 1 is a cross-sectional view (in a plane parallel to the rocker arm pivot plane) of a rocker arm and rocker stop reset assembly according to aspects of the present disclosure. [Figure 9] FIG. 1 is a cross-sectional view (in a plane parallel to the rocker arm pivot plane) of a rocker arm, a rocker stop assembly, and a damper assembly disposed within a stationary housing, the rocker arm in a valve lift position, all in accordance with aspects of the present disclosure. [Figure 10]FIG. 10 is a cross-sectional view (in a plane parallel to the rocker arm pivot plane) of a rocker stop reset assembly when the rocker arm is in a valve lift position (as shown in FIG. 9 ) according to an embodiment of the present disclosure. [Figure 11] FIG. 1 is a cross-sectional view (in a plane parallel to the rocker arm pivot plane) of a rocker arm, a rocker stop assembly, and a damper assembly disposed within a stationary housing, with the rocker arm in a stopped damping position and the damper assembly in a damping transition mode, all in accordance with aspects of the present disclosure. [Figure 12] FIG. 1 is a cross-sectional view (in a plane parallel to the rocker arm pivot plane) of a rocker arm, a rocker stop assembly, and a damper assembly disposed within a stationary housing, with the rocker arm in a stopped position and the damper assembly in a close contact dwell position, all in accordance with aspects of the present disclosure. [Figure 13] FIG. 10 is a cross-sectional view of a rocker stop reset assembly in a reset mode, according to aspects of the present disclosure. [Figure 14] FIG. 10 is a cross-sectional view of the rocker stop assembly with the actuator piston fully retracted into the actuator bore. [Figure 15] 1 is an exemplary graphical representation of a cam profile and normal and LIVC lift profiles as a function of crank angle achieved with a valve actuation system according to an aspect of the present disclosure. [Figure 16] FIG. 10 is a side perspective view of a second exemplary valve actuation system according to an embodiment of the present disclosure. [Figure 17] FIG. 17 is a top front perspective view of the second exemplary valve actuation system of FIG. [Figure 18] FIG. 10 is a cross-sectional view of a rocker stop reset assembly in a reset mode, according to aspects of the present disclosure. [Figure 19] FIG. 1 is a cross-sectional view (in a plane parallel to the rocker arm pivot plane) illustrating an example rocker stop assembly, damper assembly, and valve catch with the rocker arm in a valve lift position, according to aspects of the present disclosure. [Figure 20]1 is a cross-sectional view of a rocker arm, a rocker stop assembly, and a damper assembly disposed within a stationary housing, the rocker arm in a stopped damping position and the damper assembly in a damping transition mode. [Figure 21] FIG. 1 is a cross-sectional view of a rocker arm, a rocker stop assembly, and a damper assembly disposed within a stationary housing, the rocker arm in a stopped position and the damper assembly in a close contact dwell position, all in accordance with aspects of the present disclosure. [Figure 22] FIG. 10 is a cross-sectional view of a rocker stop reset assembly in a reset mode, according to aspects of the present disclosure. [Figure 23] FIG. 10 is a cross-sectional view of a rocker arm in valve catch mode according to aspects of the present disclosure. [Figure 24] 1 is an exemplary graphical representation of a cam profile and normal and LIVC lift profiles as a function of crank angle achieved with a valve actuation system according to an aspect of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 4 is a schematic diagram of components of a valve actuation system according to the present disclosure. Details of a specific implementation of an exemplary system according to this overview of FIG. 4 will become more apparent from the ensuing description with reference to FIGS. 5-24. High-level components and subcomponents of an exemplary embodiment according to the present disclosure may include a motion source (or cam) 1, a valve rocker assembly 7, a valve system 13, a controller 14, and a stationary housing 19. Exemplary subcomponents of each of these high-level components, as well as their functional interactions and / or relationships, are also illustrated. For example, a rocker valve assembly 7 may include a motion transmission mechanism or rocker arm 3, a rocker stop assembly 5 positioned and adapted to limit the motion of the rocker arm 3, and a reset mechanism 2 adapted to reset the rocker stop assembly 5. As a further example, the stationary housing 19 may be a stationary structure in an engine overhead environment (i.e., a rocker shaft seat that is stationary relative to rocker arm motion) and may support a hydraulic damper 18 and a valve catch 16 to control valve seating velocity, each of which may interact with the valve rocker assembly 7 to achieve LIVC and other valve motion. Specific implementations of these high-level components, sub-components, and their interactions according to this disclosure will become more apparent from the diagrams of FIGS. 5-24 and the description that follows.

[0024] Referring again to FIG. 4 , a motion source 1, which may be a cam or a push tube driven by the cam, is positioned and adapted to generate motion to drive a rocker assembly 7. A motion transmission mechanism 3 (e.g., a rocker arm) transmits motion from the cam 1 to a valve 12. In a preferred embodiment, the rocker arm 3 carries a reset mechanism 2 and a motion stop actuator 5, as described below. The valve rocker assembly is generally designated by the reference numeral 7. The cam 1 may be in direct contact with a follower on the valve rocker assembly 7 or may work in combination with a tappet or push tube to transmit motion to the rocker assembly 7. The valve rocker assembly 7 may include a reset mechanism 2 configured to maintain the rocker stop in a deployed state to achieve valve lift dwell and to reset (drop) the rocker stop at the appropriate crankshaft or cam rotation angle to achieve further (delayed) valve closure. In one embodiment, the rocker stop reset mechanism 2 may be disposed on the motion source cam side of the rocker arm 3 or may be positioned between the motion source 1 and the rocker arm 3. The reset mechanism 2 may have an internal spring arranged to bias the reset mechanism 2 against the motion source 1. This configuration allows the reset mechanism 2 to take up any lash created by the delayed closure 11 of the second mode (described below).

[0025] A controller 14, such as a programmable engine control module (ECM), provides control of the actuator energy 4 by controlling hydraulic flow and pressure to the rocker stop assembly 5 to keep the rocker stop assembly 5 deployed (extended), thus creating a motion source mismatch 6 that causes the valve to remain in a partially lifted state. The rocker stop reset mechanism 2, when pressurized by a controlled supply of hydraulic oil 4 when the valve 12 is open, can act as a check on hydraulic fluid flow from the motion stop actuator 5. When triggered into a reset mode, the rocker stop reset mechanism 2 can block, reset, or purge the actuator energy (hydraulic fluid) 4 from the rocker stop mechanism 5 to achieve valve closure. The rocker stop reset mechanism 2 can be adapted and positioned to trigger at a specific crank angle on the closing portion of the cam profile. As described in more detail below, the rocker stop reset mechanism 2 can include a reset piston or plunger that follows the cam profile. When the reset piston extends beyond a certain amount as it follows the closing portion of the cam profile, one or more reset ports on the reset piston allow hydraulic fluid to flow from the rocker stop mechanism, causing the rocker stop piston to drop or reset, further allowing the rocker to continue its valve closing motion. In embodiments illustrated in more detail below, the reset mechanism 2 can include a lash adjustment on the cam side.

[0026] Motion stop 5 may be an actuator piston slidably disposed within rocker assembly 7 and is normally biased to a retracted position unless hydraulic energy / pressure 4 causes the actuator piston to extend. The actuator follows motion source 1 to extend to the extent that valve 12 opens at peak lift. During operation, oil is checked within motion stop actuator 5 by reset mechanism 2, which reacts against hydraulic damper 18 to cock and hold the motion transfer mechanism, in this case rocker assembly 7, open until reset mechanism 2 completely purges the oil from motion stop actuator 5.

[0027] As will be appreciated, the operation of rocker stop mechanism 5, when activated, creates a mismatch 6 between motion source 1 and rocker arm 3. In other words, when rocker stop mechanism 5 is activated, the rocker arm does not follow the closing profile of motion source 1 but remains in a position corresponding to partial valve lift, thus implementing the desired LIVC operation. As rocker arm 3 bears against valve 12, thereby holding valve 12 open, and cam 1 begins to rotate through its valve closing profile, commanding rocker arm 3 and the valve to a closed position, a gap / mismatch 6 begins to form between the cam side of rocker 3 and cam 1 (or push tube or other valve train component). As a result of this gap, the reset piston within reset mechanism 2 may begin to extend to counteract the gap until a reset mode is reached, causing the rocker arm and valve to remain in a fully closed position, thus achieving LIVC.

[0028] Continuing with FIG. 4 , the valve rocker assembly 7 operates the valve system 13 in either a first (advance or normally closed) mode 9 or a second (delayed or delayed closing) mode 11. The normally closed mode 9 is characterized by the valve rocker assembly 7 and rocker arm 3 operating as commanded by the motion source 1 through the cam closing profile, with the rocker stop 5 operating in a non-actuated, non-triggered mode 8. Meanwhile, the delayed closing mode 11 is characterized by the valve rocker assembly 7 and rocker arm 3 operating as commanded by the cam 1, but with the rocker stop 5 actuated to hold the valve in a partially lifted state during the cam closing profile, followed by resetting the reset mechanism 2 to reset the rocker stop and achieve the delayed or delayed valve closing. Reference numeral 10 corresponds to the second mode, in which the valve system 13 remains open beyond the actual command of the cam 1 during valve opening, thereby opening the gap 6 between the rocker 3 and cam 1, which is then occupied by the reset mechanism 2. Reference numeral 11 denotes a delayed valve closing profile in a second mode 10 that corresponds to the same valve opening profile as the first mode 9, but in this case, the rocker arm 3 is held open until released by the reset mechanism 2, resulting in an elongated closing profile (or dwell) that causes the valves 12 to close later than normal. This LIVC dwell can occur at peak cam lift or lower lift, typically at least 3 mm of valve lift. As is known in the art, one or more valves 12 may be further engaged by a valve bridge, and a set of poppet valves 12 may be biased toward a closed position by a set of valve springs.

[0029] According to a further aspect of the present disclosure, the controller 14, via a solenoid valve and hydraulic linkage, can selectively activate a self-adjusting valve catch 16 to minimize rocker arm seating velocity during a delayed closing event 11 of the second mode 10. The valve catch 16 may be active in both the first and second modes 8 and 10, as previously described. The self-adjusting valve catch may be disposed within a stationary housing 19 and may be arranged to cooperate with the rocker arm 3.

[0030] According to a further aspect of the present disclosure, the controller 14, via a control or solenoid valve and hydraulic linkage, may selectively activate a hydraulic damper 18 that provides a smooth transition between the cam-driven closing profile and the LIVC dwell. The hydraulic damper may be disposed within a stationary housing 19 and cooperate with the rocker arm stop 5.

[0031] The details and interrelationships of the high level components and sub-components described with respect to FIG. 4 will become more apparent from the following description of specific examples and implementations in FIGS. 5-24.

[0032] 5 and 6 illustrate a first embodiment of a valve actuation system 100 including a rocker shaft seat 102 and a rocker arm 104 mounted on the rocker shaft for pivotal movement relative to the rocker shaft seat 102. For clarity, the rocker shaft is omitted from the views of FIGS. 5 and 6, but it will be appreciated that the rocker shaft is typically fixed to the rocker shaft seat 102 and extends through a journal in the rocker arm 104 to facilitate pivotal movement of the rocker arm 104 on the rocker shaft. The rocker arm 104 includes a cam (or motion source) side 106 and a valve side 108. According to aspects of the present disclosure, the motion source side 106 of the rocker arm 104 further includes and houses a rocker stop actuator assembly 110 and a rocker stop reset assembly 112, which are described in more detail below. A hydraulic passage 154 in the rocker arm 104 may provide pressurized hydraulic fluid received from a port in the rocker shaft (which further receives oil from an upstream pump and oil reservoir, as known in the art) to the rocker stop reset assembly 112. A further passage 130 in the rocker arm 104 may provide a hydraulic link between the rocker stop reset assembly and the rocker stop actuator assembly 110. The rocker stop actuator assembly 110, when hydraulically or mechanically actuated, functions to selectively limit or stop the pivotal movement of the rocker arm 104 (i.e., limiting movement in a clockwise direction as viewed in FIG. 5 ). Thus, the rocker stop actuator assembly 110 functions to stop the valve side 108 of the rocker arm 104 from reaching a position corresponding to full valve closure (i.e., thus holding the valve in a non-closed or partially lifted position for a period of time after peak lift to facilitate LIVC).

[0033] 5 and 6, and with further reference to FIG. 7, according to aspects of the present disclosure, rocker stop reset assembly 112 may include a reset plunger 114 that may be biased toward a non-reset position (i.e., maximum downward displacement relative to upper reset body 140) by a reset plunger spring 116. Reset plunger 114 extends toward a source of valve motion (not shown). Reset plunger 114 may be operatively connected to a push tube that is further operatively associated with and actuated by a cam. Rocker stop reset assembly 112 is adapted and arranged to provide resetting of rocker stop actuator assembly 110, for example, by venting hydraulic fluid from rocker stop actuator assembly 110 at an appropriate crank or cam rotation angle, thus allowing resetting (retraction) of rocker stop assembly piston 120 into bore 132, resulting in continued closing motion of the rocker arm and resulting valve closure in LIVC operation.

[0034] According to a further aspect of the disclosure, a damper assembly 118 may be housed within or extend from the rocker shaft seat and, at times, function to control the rocker stop actuator assembly 110, movement of the rocker arm 104, and thus the valve end 108 and valve movement. As described in further detail below, the damper assembly 118 is adapted and arranged to interact with the rocker stop actuator assembly 110 to provide smooth transitions in valve movement, such as transitions between normal (i.e., primary event) valve actuation movement and LIVC events. A further passageway 133 may supply hydraulic fluid from the rocker shaft to the damper assembly 118.

[0035] 7, further details of the rocker stop actuator assembly 110, the rocker stop reset assembly 112, and the damper assembly 118 are illustrated in a cross-sectional view through the motion source end 106 (FIG. 5) of the rocker arm 104. In particular, the rocker stop actuator assembly 110 may include an actuator piston 120 slidably disposed within an actuator bore 132 formed in the motion source side 106 of the rocker arm 104. As is known in the art, a lash adjustment screw 122 and a lash adjustment nut 124 are provided to allow for lash adjustment of the actuator piston 120. An actuator spring retainer 126 may be slidably disposed on the lash screw 122, and an actuator spring 128 is disposed between a shoulder on the lash screw 122 and the actuator spring retainer 126, such that in the absence of any hydraulic actuation of the actuator piston 120 (i.e., suitable hydraulic pressure in the bore 132), the actuator piston 120 is biased to retract into the actuator bore 132.

[0036] Actuation of the rocker stop actuator assembly 110 may be controlled through a hydraulic actuation circuit or linkage comprising various passages within valve train components, as described in more detail below. The hydraulic actuation circuit may include a first hydraulic passage 130 in hydraulic communication with an actuator bore 132. While not shown in FIG. 7 , the first hydraulic passage 130 is in fluid communication with a second hydraulic passage 158 ( FIG. 8 ) by way of an additional passage in the rocker arm (i.e., a flycut region connecting passage 158 to passage 130), which may allow for selective (e.g., under control of a solenoid valve) supply of hydraulic fluid to the first hydraulic passage 130 and the actuator bore 132 to actuate the rocker stop assembly. As will be appreciated, such additional passage may provide fluid communication from passage 158 to passage 130 and the actuator bore 132 regardless of the state (reset mode or non-reset mode) of the rocker stop reset assembly.

[0037] Rocker stop reset assembly 112 includes an upper reset body 140 and a separate lower reset body 144, both of which may be fastened to rocker arm 104 with threaded fittings and both of which have internal bores to guide and allow sliding movement of reset plunger 114. Upper reset body 140 may include a lash adjustment screw (and corresponding lash adjustment nut 142) to facilitate lash adjustment of reset plunger 114. Lower reset body 144 is fixedly attached (e.g., by threaded engagement) to rocker arm 104 such that reset plunger 114 extends out of lower reset body 144 toward (i.e., downward in FIG. 7 ) a source of valve actuation motion (e.g., a push tube and cam, not shown). The reset plunger spring 116 is positioned between respective shoulders formed in the lower reset body 144 and a lower portion of the reset plunger 114 such that the reset plunger 114 is biased into contact with the source of motion (i.e., biased downward in FIG. 7 ). Upward travel of the reset plunger 114 (i.e., into the longitudinal channel formed in the upper reset body 140) is restricted when tight contact occurs between the lower reset body shoulder 150 and the reset plunger shoulder 152. As shown, the reset plunger 114 further includes a drain passage 146 formed therein and configured to provide fluid communication with the ambient atmosphere, and an oil return path within the engine overhead environment (i.e., drip / flow into and through the overhead environment via an appropriate passage to the oil pan). As will be described in more detail with respect to FIG. 8, a reset port 148 is provided as a radial opening (i.e., a radially extending port) formed in the reset plunger 114 and in fluid communication with the exhaust passage 146.

[0038] 8 illustrates, in cross-section, further details of rocker stop reset assembly 112 and rocker arm 104. As shown, rocker arm 104 includes a fourth hydraulic passage 154 configured to receive hydraulic fluid selectively applied from a rocker arm shaft (not shown) using known techniques. A check valve assembly 156 provides one-way fluid communication between fourth hydraulic passage 154 and second hydraulic passage 158. A spill port 160 formed in upper reset body 140 provides selective (i.e., dependent on the position of lower reset body 144) hydraulic communication with the volume established by actuator bore 132, first hydraulic passage 130, and second hydraulic passage 158.

[0039] As described in more detail below, in the extended mode of rocker arm stop assembly 110, reset plunger 114 may be in the lowered position shown in FIG. 7 relative to upper reset body 140, and the outer diameter of reset plunger 114 may seal second hydraulic passage 158, thereby sealing the volume established by actuator bore 132, first hydraulic passage 130, and second hydraulic passage 158. During such operation, pressurized hydraulic fluid from fourth hydraulic passage 154 enters actuator bore 132 and overcomes the bias exerted by actuator piston spring 128, thereby extending actuator piston 120 from actuator bore 132.

[0040] According to aspects of the present disclosure, rocker stop reset assembly 140 facilitates a reset mode of rocker arm stop assembly 110, whereby as reset plunger 114 translates (i.e., moves downward in FIG. 7 ) within upper reset housing 140 (due to the application of valve actuation motion), reset port 148 formed within reset plunger 114 periodically aligns with spill port 160. During such movement, hydraulic fluid trapped within actuator bore 132 is allowed to escape via the flow path established by first hydraulic passage 130, second hydraulic passage 158, spill port 160, reset port 148, and drain passage 146, thereby allowing actuator piston 120 to retract back into actuator bore 132.

[0041] Damper assembly 118 includes a damper piston 134 and a base 136. A third hydraulic passage 133 is provided in rocker shaft seat 102 and supplies hydraulic fluid through an opening 135 in base 136 into the space between base 136 and damper piston 134. As further shown, damper piston 134 also includes a protrusion 137 that is aligned with and capable of sealing opening 135 when protrusion 137 abuts base 136. The provision of pressurized hydraulic fluid to damper assembly 118 may be continuous or may be selectively switched by a suitable control device (e.g., a solenoid). When hydraulic fluid is present in the space between damper piston 134 and base 136, downward pressure exerted on damper piston 134 by actuator piston 120 causes the hydraulic fluid to escape through opening 135 back into third hydraulic passage 133. Continued downward translation of damper piston 134 and protrusion 137 gradually reduces the flow area between the protrusion and opening 135, thereby gradually slowing the flow of hydraulic fluid and therefore the translational speed of damper piston 134 until the point at which protrusion 137 abuts base 136, thereby stopping any further translation of damper piston 134.

[0042] FIG. 15 illustrates an intake cam profile 170 suitable for use in conjunction with the embodiment illustrated in FIGS. 5-14. In particular, cam profile 170 illustrates a main intake event 172 that facilitates positive power generation in fueled cylinders of an internal combustion engine, as is known in the art. Cam profile 170 further includes a so-called sub-base circle feature that includes a second closing ramp 174 used during LIVC operation of valve actuation system 100 of FIGS. 5-8. During normal main event 172 operation, hydraulic fluid is not provided to actuator bore 132, thereby preventing extension of actuator piston 120. As a result, actuator piston 120 does not engage damper piston 134, thereby allowing the rocker arm to close according to first closing ramp 176 in the normal manner, i.e., without LIVC operation. However, during LIVC operation, hydraulic fluid is provided to (and trapped within) actuator bore 132 so that actuator piston 120 is maintained in its extended position, thereby maintaining the engine valve in an open position 180 to provide the desired LIVC operation. The interaction of actuator piston 120 and damper piston 134 ( FIG. 7 ) provides a smooth transition 178 between main event lift 172 and LIVC dwell 180. As described in further detail below, subsequent operation of rocker stop reset assembly 112 drops actuator piston 120, thereby providing a closure event 182 commanded by second closure ramp 174.

[0043] Further operation of the embodiment illustrated in Figures 5-8, particularly during LIVC operation, is further illustrated with reference to Figures 9-15. Figure 9 illustrates the state of the actuator piston 120 and damper piston 134 during the opening ramp of the primary event 172 (as shown in Figure 15) and prior to the LIVC transition 178. During this time, the primary event lift 172 provides sufficient space between the actuator piston 120 and the damper piston 134 to allow hydraulic fluid to fill the actuator bore 132, thereby extending the actuator piston 120 to its maximum position (in this example, as determined by intimate contact between the actuator piston spring retainer 126 and the shoulder 162 formed on the lash screw 122).

[0044] 9, simultaneously with extension of actuator piston 120, hydraulic fluid provided to damper assembly 118 via third hydraulic passage 133, under the control of, for example, a control valve and / or a port on the rocker shaft, flows through opening 135 to fill the space between base 136 and damper piston 134, thereby causing damper piston 134 to extend out of its bore, i.e., generally toward rocker arm 104 and actuator piston 120 (i.e., upward in FIG. 9). As further shown in FIG. 9, in addition to opening 135, checked passage 164 may be provided in base 136 so that fluid may more quickly fill the space between base 136 and damper piston 134 during valve opening.

[0045] 10 illustrates the operation of the reset assembly and plunger 114 during the same period depicted in FIG. 9 , i.e., during valve opening and before the LIVC transition 178. During this time, the valve lift provided by the primary event 172 overcomes any bias applied by the reset plunger spring 116, thereby translating the reset plunger 114 upward to intimate contact between the respective shoulders 150, 152 of the lower reset body 144 and the reset plunger 114, as shown. Notably, this upward translation of the reset plunger 114 advances the reset port 148 past the spill port 160, which is instead sealed by the outer diameter of the reset plunger 114, as shown. As a result, hydraulic fluid within the actuator bore 132 is prevented from being exhausted and instead maintains the actuator piston 120 in its extended position.

[0046] 11, there is shown the state of the actuator piston 120 and damper piston 134 when they contact each other at full extension during the closing ramp of primary event 172. Referring to the example illustrated in FIG. 15, this occurs at approximately 6 mm of intake valve lift (assuming zero valve lash) or approximately 520 degrees of crank angle. Furthermore, in this example, the stroke length of the damper piston 134 (i.e., the distance between the damper piston 134 and the base 136 when the damper piston 134 is fully extended) is assumed to be 2 mm.

[0047] As the hydraulic damper piston 134 is pushed down by the fully extended actuator piston 120, hydraulic fluid is forced out through an opening 135 in the hydraulic damper base 136. The curtain flow area between the hydraulic piston lower projection 137 and the opening 135 gradually decreases as the damper piston 134 moves downward, throttling the flow of hydraulic fluid back into the third hydraulic passage 133 and providing a smooth transition 178 to the LIVC “back porch” dwell 180 ( FIG. 15 ). The dwell 180 is then provided when the damper piston 134 establishes intimate contact with the base 136, thereby causing the fully extended actuator piston 120 to hold the rocker arm (and, consequently, the intake valve) in an open position. FIG. 12 illustrates this LIVC back porch lift state or dwell 180, in which the damper piston 134 bottoms out on the base 136 while the actuator piston 120 remains in its fully extended position. As shown in the example of FIG. 15, dwell 180 is maintained at approximately 3.5 mm of intake valve lift for a crank angle of approximately 60-70 degrees.

[0048] During the transition period 178 and the LIVC dwell 180, a mismatch or gap 184 (or 1284 in FIG. 24 ) occurs between the lift maintained on the intake valve and the cam profile 170. As shown in FIG. 13 , this allows the reset plunger 114, under the bias applied by the reset plunger spring 116, to follow the cam profile 170 ( FIG. 15 ), thereby translating downward within the longitudinal channel formed in the upper reset body 140. This is illustrated in FIG. 13 by the resulting gap between the lower reset body 144 and the reset plunger 114. This process of the reset piston 114 following the cam profile 170 while the rocker arm 104 and intake valve are maintained in the LIVC dwell 180 continues until such time as the reset port 148 begins to align with the spill port 160. As shown in FIG. 13 , once a slight overlap is provided between the reset port 148 and the spill port 160, pressurized fluid trapped within the actuator bore 132 (and the first and second hydraulic passages 130, 158) can be vented to atmosphere through the flow path provided by the spill port 160, the reset port 148, and the drain passage 146. This, in turn, allows the actuator piston 120 to retract back into the actuator bore 132 at a rate determined by the rate of fluid venting through the spill port 160, the reset port 148, and the drain passage 146. As the actuator piston 120 retracts, the rocker arm 104 rotates toward the cam, while the reset plunger 114 simultaneously follows the cam profile 170. In this case, the reset piston 114 “hesitates” such that the reset port 148 and the spill port 160 are maintained in this slight overlapping positioning while the rocker arm 104 continues to rotate toward valve closure. In this manner, the valve lift closing event 182 is effectively commanded by the closing ramp 174 of the cam profile 170. This gradual valve closing process continues until the actuator piston 120 is fully retracted into the actuator bore 132, as illustrated in FIG.

[0049] FIGS. 16 and 17 illustrate a second embodiment of a valve actuation system 1200. Like reference numerals depicted in FIGS. 5, 6, 16, and 17 refer to structure that is structured and operates substantially similarly. Accordingly, the rocker stop actuator assembly 1110 and the damper assembly 1118 may be substantially similar to the rocker stop actuator assemblies 1110 and 1118 in the first embodiment. In contrast, as described below, the reset assembly 1212 may be structured and operate somewhat differently compared to the first embodiment illustrated in FIGS. 5 and 6. Additionally, a self-adjusting valve catch (SAVC) 1300 is provided in the second embodiment illustrated in FIGS. 16 and 17. The SAVC assembly 1300 may be substantially similar in construction and operation to the self-adjusting valve catch disclosed in U.S. Pat. No. 8,079,338, the entire disclosure and teachings of which are incorporated herein by reference.

[0050] 18 illustrates, in cross-section, further details of the reset assembly 1212 and rocker arm 1104 according to the second embodiment. Here, the rocker arm 1104 again includes a fourth hydraulic passage 1154, a check valve assembly 1156, and a second hydraulic passage 1158, while the rocker stop reset assembly 1112 again includes an upper reset body 1140 and a lower reset body 1144. However, in this embodiment, the reset plunger 1214 extends only through a longitudinal channel formed in the lower reset body 1144, and a reset plug 1241 is provided having a reset port 1248 formed therein. In this case, the reset plug 1241 is fixedly maintained within the longitudinal channel formed in the upper reset body 1140 such that the reset port 1248 is continuously aligned with a spill port 1160 formed in the upper reset body 1140. The reset plug 1241 further comprises a central passage 1242 in fluid communication with the reset port 1248 .

[0051] A reset piston 1245 is slidably disposed within a longitudinal channel formed in the upper reset body 1140. As shown, the reset piston 1245 has a central upper surface 1247 that aligns with the central passage 1242 of the reset plug 1241. The reset piston 1245 further comprises one or more channels 1249 extending from the periphery of the central upper surface 1247 and providing fluid communication with an interior region of the reset piston 1245. The reset piston 1245 is biased into contact with the reset plug 1241 by a reset piston spring 1251 disposed between the reset piston 1245 and the reset plunger 1214. As shown, the interior region of the reset piston 1245 is further in fluid communication with a drain passage 1246 formed in the reset plunger 1214. If the biasing force exerted by the reset piston spring 1251 is greater than any opposing hydraulic pressure exerted on the reset piston 1245 through the central passage 1242, the reset piston 1245 will remain abutting against the reset plug 1241, thereby preventing any fluid flow through the central opening 1242, the channel 1249, and the discharge passage 1246.

[0052] FIG. 24 illustrates an intake cam profile 1270 suitable for use in conjunction with the second embodiment illustrated in FIGS. 16-23. In particular, the cam profile 1170 illustrates the main intake event 1172 as described above. The cam profile 1270 further includes a closing ramp 1176. Again, during normal main event 1172 operation, hydraulic fluid is not provided to the actuator bore 1132 ( FIG. 19 ), thereby preventing the actuator piston 1120 from extending. As a result, the actuator piston 1120 does not engage the damper piston 134, thereby allowing the rocker arm to close 1176 in the normal manner, i.e., without LIVC operation. However, during LIVC operation, hydraulic fluid is still provided to (and captured within) the actuator bore 1132, such that the actuator piston 1120 is maintained in its extended position, thereby maintaining the engine valve in an open position 1280 to provide the desired LIVC operation. The interaction of the actuator piston 1120 and the damper piston 1134 similarly provides a smooth transition 1278 between the main event lift 1172 and the LIVC dwell 1280. As described in more detail below, subsequent operation of the reset assembly 1212 drops the actuator piston 1120, thereby providing a closing event 1282 and valve seating profile 1283 controlled by the SAVC 1300, as described in more detail below.

[0053] 18, the state of the reset plunger 1214 and reset piston 1245 is shown during the opening ramp of the primary event 1172 (as shown in FIG. 24) and before the LIVC transition 1278. That is, despite the presence of fluid in the second hydraulic passage 1158 and the reset port 1248, the bias of the reset piston spring 1251 is sufficient to maintain the reset piston 245 in sealing engagement with the central passage 1242, which in turn allows the actuator piston 1120 to extend out of the actuator bore 1132, as previously described.

[0054] 19 , concurrent with extension of actuator piston 1120, hydraulic fluid provided to damper assembly 1118 via third hydraulic passage 1133 flows through opening 1135, past protrusion 1137, and fills the space between base 1136 and damper piston 1134, thereby extending damper piston 1134 as described above. As further shown, third hydraulic passage 1133 also extends to SAVC assembly 1300, which in this embodiment operates essentially identically to damper assembly 1118, except in the opposite manner in this embodiment. That is, as shown, SAVC assembly 1300 includes a slidable SAVC base 1302 disposed within SAVC bore 304 in fluid communication with third hydraulic passage 133. An internal chamber 1307 is formed in SAVC base 1302, and an opening 1306 (along with an optional checked passageway, as shown) provides fluid communication between third hydraulic passageway 1133 and internal chamber 1307. SAVC plunger 1308 is disposed within the internal chamber and is biased upward toward opening 1306 by SAVC plunger spring 1310. SAVC plunger 1308 further includes a protrusion 1309 that aligns with opening 1306. As shown, hydraulic pressure provided by third hydraulic passageway 1133 causes fluid to enter internal chamber 1307, and the fluid is sufficiently pressurized to overcome any biasing force exerted by SAVC plunger spring 1310, thereby disengaging protrusion 1309 from opening 1306. Additionally, as described in U.S. Pat. No. 8,079,338, leakage of pressurized hydraulic fluid through the SAVC plunger 1308 results in a substantially consistent volume of fluid being filled within the space formed by the interior region of the SAVC plunger 1308 and the walls of the SAVC bore 1304.

[0055] 20, there is shown the state of the actuator piston 1120 and damper piston 1134 when they contact each other at full extension during the closing ramp of primary event 1172. Referring to the example illustrated in FIG. 24, this again occurs at approximately 6 mm of intake valve lift (assuming zero valve lash) or approximately 1520 degrees crank angle. Furthermore, in this example, the stroke length of the damper piston 1134 is also assumed to be 2 mm.

[0056] As explained above, the continued interaction between the fully extended actuator piston 1120 and the damper piston 1134 provides a smooth transition 1278 to the LIVC "back porch" dwell 1280. Again, the dwell 1280 is provided when the damper piston 1134 bottoms out with the base 1136, thereby causing the fully extended actuator piston 1120 to hold the rocker arm (and thus the intake valve) in an open position. FIG. 21 illustrates this LIVC back porch lift state or dwell 1280, where the damper piston 1134 bottoms out on the base 1136 while the actuator piston 1120 remains in its fully extended position. As shown in the example of FIG. 24, the dwell 1180 is maintained at approximately 3.5 mm of intake valve lift for approximately 20-30 degrees of crank angle.

[0057] Again, during the transition period 1278 and the LIVC dwell 1280, a mismatch or gap 1276 occurs between the lift maintained on the intake valve and the cam profile 270. As shown in FIG. 22 , this allows the reset plunger 1214, under the bias applied by the reset plunger spring 1116, to follow the cam profile 1170, particularly the closure ramp 1176, thereby translating downward within the longitudinal channel formed in the lower reset body 1144. This is illustrated in FIG. 22 by the resulting gap between the lower reset body 1144 and the reset plunger 1214. This process of the reset piston 1214 following the cam profile 1270 while the rocker arm 1104 and intake valve are maintained in the LIVC dwell 1280 continues until such time that the spring force applied by the reset piston spring 1251 falls below the hydraulic pressure applied to the reset piston 1245, thereby translating the reset piston 1245 downward. This further opens a fluid path through the spill port 1160, the reset port 1248, and the channel 1249 into the exhaust passage 1246. In this case, unlike the "hesitation" embodiment described above, the spill port 1160 remains substantially open due to the large increase in hydraulic pressure pushing on the reset piston 1245 due to the large increase in pressure area and the fact that most of the pressure drop occurs across the channel 1249 formed in the reset piston 1245. As a result, the actuator piston 1120 retracts fairly quickly into the actuator bore 1132, which in turn causes the rocker arm 1104 and intake valve to close equally quickly, potentially leading to undesirable jolts during valve seating.

[0058] To this end, the SAVC assembly 1300 operates to engage the rocker arm 1104 and provide a gradual valve seating event 1283. In particular, as the rocker arm 1104 rotates toward the source of motion, the rocker arm extension 1340 engages the SAVC base 1302, thereby forcing the SAVC base 1302 into the SAVC bore 1304 and compressing hydraulic fluid in the internal chamber 1307. At the same time, however, the volume of fluid trapped behind the SAVC plunger 1308 prevents the SAVC plunger 1308 from retracting further into the SAVC bore 1304. As a result, when the SAVC base 1302 is displaced downward, the lack of relative movement of the SAVC plunger 1308 forces hydraulic fluid from the decreasing volume of the internal chamber 1307 through the opening 1306 and back into the third hydraulic passageway 1133. As the SAVC base 1302 approaches the SAVC plunger 1308, the continuously decreasing flow area between the protrusion 1309 and the opening 1306 increases the resistance to the escaping hydraulic fluid, thereby smoothly slowing further downward movement of the SAVC base 1302. This process continues until the protrusion 1309 fully engages and seals the opening 1306, as shown in FIGURE 23, thereby preventing further escape of hydraulic fluid and further downward movement of the SAVC base 1302. As further shown in FIGURE 23, the gradual valve closing process also continues until the actuator piston 1120 is fully retracted into the actuator bore 1132.

[0059] While specific embodiments have been shown and described, those skilled in the art will understand that changes and modifications can be made without departing from the present teachings. Accordingly, any and all modifications, variations, or equivalents of the teachings set forth above are deemed to fall within the scope of the basic underlying principles disclosed above.

[0060] For example, while the rocker stop actuator piston in the described embodiment is disposed within the rocker arm, it will be appreciated that other arrangements are within the scope of this disclosure. For example, the rocker stop actuator piston may be located within the fixed housing (rocker shaft seat) and arranged to contact the cam side of the rocker arm. Alternatively, the rocker stop may be disposed on the valve side of the rocker arm and configured and adapted to be disposed therein or within the fixed housing.

Claims

1. A valve actuation system for actuating at least one engine valve of an internal combustion engine, said valve actuation system comprising: a rocker for imparting motion to the at least one engine valve; a motion source positioned to impart motion to a motion-source side of the rocker, the motion source defining a main event peak lift of the at least one engine valve; and a rocker stop assembly at least partially coupled to a cylinder head of the internal combustion engine, the rocker stop assembly configured to operate in an active mode that initially allows the motion source side of the rocker to move as commanded by the motion source and, after the main event peak lift, maintains the motion source side of the rocker at a position corresponding to a valve lift, whereby the motion source side of the rocker is not commanded by a motion source closing profile, and a non-active mode that allows the motion source side of the rocker to move as commanded by the motion source to a position corresponding to a fully closed valve position; a rocker stop reset assembly adapted to reset the rocker stop assembly to the non-operating mode based on a position of the rocker relative to the motion source and following the primary event peak lift, thereby achieving delayed valve closure.

2. The valve actuation system of claim 1 , wherein the rocker stop assembly is disposed within the rocker.

3. The valve actuation system of claim 1 , wherein the rocker stop assembly is disposed on a cam side of the rocker.

4. The valve actuation system of claim 1 , wherein the rocker stop assembly comprises a hydraulically actuated piston.

5. 2. The valve actuation system of claim 1, wherein the rocker stop reset assembly is adapted to reset the rocker stop assembly to the non-operating mode at a predetermined angle of rotation of an engine crankshaft or cam.

6. 2. The valve actuation system of claim 1, wherein the rocker stop reset assembly comprises a plunger adapted to extend to occupy lash between the motion source and the rocker, the plunger further adapted to reset the rocker stop assembly to the non-operating mode when the plunger extends to a reset position.

7. The valve actuation system of claim 1 , wherein the rocker stop reset assembly is adapted to hold the rocker stop assembly in the run mode during a portion of the closing profile of the motion source.

8. 2. The valve actuation system of claim 1, wherein the source of motion is a single cam lobe.

9. 10. The valve actuation system of claim 1, further comprising a damper assembly positioned to interact with the rocker stop assembly and adapted to provide a smooth transition of the rocker and valve motion to a delayed intake valve closing dwell.

10. 10. The valve actuation system of claim 9, wherein the damper assembly is disposed within a housing fixed relative to the rocker.

11. 10. The valve actuation system of claim 1, further comprising a valve catch assembly disposed to interact with the rocker and adapted to control a seating velocity of the at least one valve.

12. 12. The valve actuation system of claim 11, wherein the valve catch assembly is disposed within a housing fixed relative to the rocker.

13. 12. The valve actuation system of claim 11, wherein the valve catch assembly is positioned to interact with a protrusion on a cam side of the rocker.

14. The valve actuation system of claim 1 , wherein the rocker stop assembly and the rocker stop reset assembly are disposed on a cam side of the rocker.

15. 2. The valve actuation system of claim 1, wherein the rocker stop assembly and the rocker stop reset assembly are connected through at least one hydraulic passage.

16. 2. The valve actuation system of claim 1, wherein the motion source includes a sub-base circle cam profile having a closing ramp, and the rocker stop reset assembly is adapted to allow the rocker stop assembly to fall at a rate such that the rocker follows the sub-base circle cam profile closing ramp.

17. 2. The valve actuation system of claim 1, wherein the rocker stop reset assembly is adapted to reset the rocker stop assembly to the non-operating mode based on a lift of a motion source and to fall at a rate independent of the motion source.

18. 18. The valve actuation system of claim 17, wherein the rocker stop reset assembly comprises a spring-biased reset piston adapted to retain hydraulic fluid within the rocker stop assembly in the active mode and to vent hydraulic fluid from the rocker stop assembly to ambient in the non-active mode, the reset piston adapted to remain open while the rocker stop assembly is dropped.

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