JP7652939B2 - Valve actuation system including a pre-rocker arm valve train component and an in-line lost motion component disposed on a valve bridge - Google Patents

Description

The present disclosure relates generally to valve actuation systems, and more particularly to valve actuation systems having lost motion components in series along the valve actuation load path, which may be used to implement both cylinder deactivation and auxiliary valve actuation.

Valve actuation systems for use in internal combustion engines are well known in the art. During positive power operation of an internal combustion engine, such valve actuation systems are used to provide a so-called primary valve actuation motion to the engine valves in conjunction with the combustion of fuel, so that the engine outputs power that can be used, for example, to operate a vehicle. Alternatively, the valve actuation systems may be operated to provide a so-called auxiliary valve actuation motion other than, or in addition to, the primary valve actuation motion. The valve actuation systems may also be operated in such a manner to stop operation of a given engine cylinder at once, i.e., not operating in either primary or auxiliary mode, by removing engine valve actuation, often referred to as cylinder deactivation. As is further known in the art, these various modes of operation may be combined to provide desired benefits. For example, future emission standards for heavy duty diesel trucks require technologies that improve fuel economy and reduce emissions. A key technology that provides both simultaneously is cylinder deactivation. It is well documented that cylinder deactivation reduces fuel consumption, increases temperatures, and improves control of aftertreatment emissions.

A known system for cylinder deactivation is described in U.S. Pat. No. 9,790,824, which describes a hydraulically controlled lost motion mechanism disposed on a valve bridge, an example of which is illustrated in FIG. 11 of the '824 patent and reproduced herein as FIG. 1. As shown in FIG. 1, the lost motion mechanism includes an outer plunger 120 disposed with a bore 112 formed in a body 110 of a valve bridge 100. A locking element in the form of a wedge 180 is provided, which is configured to engage an annular outer recess 172 formed in a surface defining the bore 112. When no hydraulic control is applied to the inner plunger 160 (in this case via a rocker arm, not shown), the inner piston spring 144 biases the inner plunger 160 into a predetermined position such that the wedge 180 extends from an opening formed in the outer plunger 120, thereby engaging the outer recess 172 and effectively locking the outer plunger 120 in position relative to the valve bridge body 110. In this state, valve actuation motion (primary or secondary) applied to the valve bridge via the outer plunger 120 is transferred to the valve bridge body 110 and ultimately to the engine valve (not shown). However, providing sufficient pressurized hydraulic fluid to the top of the inner plunger 160 causes the inner plunger 160 to slide downward, thereby allowing the wedge 180 to retract and disengage from the outer recess 172, thereby effectively unlocking the outer plunger 120 relative to the valve bridge body 110 and allowing the outer plunger 120 to slide freely within its bore 112, subject to the bias provided by the outer plunger spring 146 toward the rocker arm. In this state, valve actuation motion applied to the outer plunger 120 causes it to reciprocate within its bore 112. Thus, assuming the movement of the outer plunger 120 within the bore 112 is greater than the maximum range of the applied valve actuation motion, such valve actuation motion is not transferred to the engine valve and is effectively lost such that the corresponding cylinder is deactivated.

However, one drawback of deactivating cylinders is that the airflow through the engine is reduced, which also reduces the energy in the exhaust system. During vehicle warm-up from a cold start, it is important to increase the exhaust temperature to quickly bring the catalyst temperature up to an efficient operating temperature. While cylinder deactivation provides a temperature increase, the significant reduction in airflow is not effective for a quick warm-up.

To overcome this drawback of cylinder deactivation and provide a quicker warm-up, one proven technique is to advance the opening of the exhaust valve to release additional thermal energy to the exhaust system, called early exhaust valve opening (EEVO), which is a specific type of auxiliary valve actuation motion in addition to the main valve event. In effect, such systems are based on the principle of providing this early opening event by adding valve actuation motion that is lost during the main valve actuation. Systems that combine both early exhaust opening and cylinder deactivation features can meet warm-up requirements, reduce emissions, and improve fuel consumption.

A valve actuation system for providing EEVO may be provided using a rocker arm having a hydraulically controlled lost motion component in the form of an actuator, as illustrated in U.S. Pat. No. 6,450,144, an example of which is illustrated in FIG. 19 of the '824 patent and reproduced herein as FIG. 2. In this system, a rocker arm 200 is provided having an actuator piston 210 disposed at the motion-imparting end of the rocker arm 200. The actuator piston 210 is biased from its bore by a spring 217 such that the actuator piston 210 is in continuous contact with a corresponding engine valve (or valve bridge). Hydraulic passages 231, 236 are provided to allow hydraulic fluid to be supplied by the control passage 211 to fill the actuator piston bore. In these circumstances, hydraulic fluid is retained in the bore by a check valve 241, and unless the hydraulic passage 236 is aligned with the control passage 211, in which case the actuator piston 210 is rigidly maintained in an extended position and cannot reciprocate within its bore. On the other hand, if the bore is not filled with hydraulic fluid (or such hydraulic fluid is evacuated upon alignment of the noted passages 236, 211), the actuator piston 210 is free to reciprocate within its bore to the extent permitted by the lash adjustment screw 204. In such a system, the cam includes cam lobes to provide both primary and secondary valve actuating motions. In primary valve actuation, no hydraulic fluid is provided to the actuator piston 210 so that the actuator piston 210 is permitted to reciprocate within its bore. In this case, to the extent that the amount of movement permitted by the actuator piston 210 into its bore is at least as great as the maximum motion provided by the EEVO lobe, but less than the maximum motion provided by the primary event lobe, the valve actuation motion provided by the EEVO lobe is lost due to the reciprocating motion of the actuating piston 210, but actuation of the primary event valve will cause the actuating piston 210 to bottom out in its bore (or via solid contact with another surface), thereby transmitting the primary event motion. On the other hand, position-based exhaust of the actuator bore (i.e., resetting by alignment of passages 236, 211 as noted) prevents over-extension of the engine valve during main valve event motion, but if the actuator piston is hydraulically locked in the extended position, the EEVO motion is not lost and is transmitted to the engine valve.

In theory, at least, it should be possible to combine lost-motion based cylinder deactivation with an auxiliary valve actuation motion system of the type described above to provide the desired cylinder deactivation and EEVO operation. However, there is no evidence that simply directly combining such systems would provide the desired results.

For example, as noted above, EEVO lost motion combines normal main event lift with an early rise on the same camshaft. An example of this is illustrated in FIG. 3. In FIG. 3, a first curve 310 illustrates an idealized version of the main event valve lift, in this example with a maximum lift of about 14 millimeters. A second curve 311 illustrates a typical actual main event experienced by an engine valve that would occur when the EEVO motion provided by the cam is lost, e.g., the rocker arm actuator described above in FIG. 2 can reciprocate. The upper dashed curve 312 illustrates the ideal valve lift if, for example, all the valve actuation motion provided by the EEVO-enabled cam is provided when the rocker arm actuator is fully extended. As shown, the idealized lift 312 includes an EEVO event 313 of about 3 mm of valve lift during valve opening, which actually translates to about 2 millimeters of valve lift 314. The example illustrated in FIG. 3 also shows the occurrence of a reset, which allows the actuator piston to drop, in this example, at about 10 mm of lift (i.e., the locked hydraulic fluid in the actuator bore is vented for this cycle of the engine valve), thereby generating a normal lift main event 311. The combination of these two lift events (as illustrated by the ideal lift profile 312) results in a total stroke of about 17 mm, which, if lost due to the lost motion mechanism illustrated in FIG. 1, places a relatively high stress on the outer plunger spring 146 as it attempts to bias the outer plunger 120 through the entire 17 mm of its travel.

As an additional example, it is known that during cylinder deactivation as described above, the normal force applied by the engine valve spring to bias the rocker arm into continuous contact with the source of valve actuation motion (e.g., cam) is no longer provided. Although the outer piston plunger spring 146 provides some force back toward the rocker arm via the outer plunger 120, this force is relatively small and insufficient to control the rocker arm as needed. Thus, a separate rocker arm biasing element is typically provided to bias the rocker arm into contact with the cam, for example, by applying a bias force toward the cam at the motion-receiving end of the rocker arm via a spring located above the rocker arm. Failure to adequately control the inertia presented by the rocker arm (due to the valve actuation motion still applied to the rocker arm despite being deactivated) can result in separation of the rocker arm and the cam, resulting in detrimental effects between the two. Similarly, the EEVO valve actuation motion that is lost when EEVO operation is not required imparts inertia to the rocker arm that must be controlled as well. A complicating factor in these actions due to the rocker arm biasing element is that each of these actions (cylinder deactivation and EEVO) typically occurs at significantly different speed ranges.

Normally, cylinder deactivation typically occurs at engine speeds below about 1800 rpm, and the rocker arm biasing element is configured to provide sufficient force at these speeds to ensure proper contact between the rocker arm and the cam. On the other hand, lost EEVO valve actuation motion exists up to high engine speeds (e.g., on the order of 2600 rpm). Therefore, to obtain the combined benefits of cylinder deactivation and EEVO operation, the rocker arm biasing element must accommodate the high speeds at which the EEVO valve actuation motion can still be applied to the rocker arm. Because of the relatively high speeds at which they can still occur, rocker arm control over lost EEVO valve actuation motion requires the application of high forces by the rocker arm biasing element. However, this occurs at small valve lifts where the rocker arm bias spring has its lowest preload. On the other hand, cylinder deactivation typically occurs at low speeds throughout the higher lift portion (main valve actuation motion) where the rocker arm biasing element is at increased preload. However, the challenge of providing a rocker arm biasing element that can provide high force with minimal preload (required for EEVO) and withstand the stresses required during full travel (required for cylinder deactivation) is difficult to overcome.

The above-mentioned shortcomings of the prior art solutions are addressed by providing a valve actuation system for actuating at least one engine valve in accordance with the present disclosure. In particular, the valve actuation system includes a valve actuation motion source configured to provide a main valve actuation motion and an auxiliary valve actuation motion for actuating at least one engine valve via a valve actuation load path. A lost motion subtraction mechanism is disposed in the pre-rocker arm valve train component and configured to transfer at least the main valve actuation motion in a first default operating state and to lose the main valve actuation motion and the auxiliary valve actuation motion in the first operating state. Additionally, a lost motion adder mechanism is disposed in the valve bridge and configured to lose the auxiliary valve actuation motion in a second default operating state and to transfer the auxiliary valve actuation motion in the second operating state, where the lost motion adder mechanism is in series with the lost motion subtracter mechanism in the valve actuation load path.

Examples of auxiliary valve actuation motions include at least one of an early exhaust valve opening valve actuation motion, a late intake valve closing valve actuation motion, or an engine braking valve actuation motion.

In one embodiment, the valve actuation system further includes an engine controller configured to operate the internal combustion engine using a lost motion subtraction mechanism and a lost motion addition mechanism. In a positive power mode, the engine controller controls the lost motion subtraction mechanism to operate in a first default operating state and the lost motion addition mechanism to operate in a second default operating state. In a pause mode, the engine controller controls the lost motion subtraction mechanism to operate in a first working operating state and the lost motion addition mechanism to operate in a second default operating state. In an assist mode, the engine controller controls the lost motion subtraction mechanism to operate in a first default operating state and the lost motion addition mechanism to operate in a second working operating state.

Corresponding methods are also disclosed.

The features described in this 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 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:
1 illustrates a lost motion mechanism suitable for providing cylinder deactivation according to the prior art. 1 illustrates a lost motion mechanism suitable for providing auxiliary valve actuation according to the prior art. 1 is a graph illustrating an example of EEVO valve actuation motion according to the present disclosure. 1 is a schematic illustration of an embodiment of a valve actuation system according to the present disclosure. 1 is a schematic illustration of an embodiment of a valve actuation system according to the present disclosure. 5 illustrates a partial cross-sectional view of an embodiment of a valve actuation system according to the embodiment of FIG. 4. FIG. 7 is an exploded view of the reset rocker arm according to the embodiment of FIG. 9A-9C are partial top and side cross-sectional views, respectively, of a reset rocker arm according to the embodiment of FIGS. 6-8. 9A-9C are partial top and side cross-sectional views, respectively, of a reset rocker arm according to the embodiment of FIGS. 6-8. 9A-9C are partial top and side cross-sectional views, respectively, of a reset rocker arm according to the embodiment of FIGS. 6-8. 9A-9C are partial top and side cross-sectional views, respectively, of a reset rocker arm according to the embodiment of FIGS. 6-8. FIG. 6 is a partial cross-sectional view of a first embodiment of a valve actuation system in accordance with the embodiment of FIG. FIG. 6 is a partial cross-sectional view of a second embodiment of a valve actuation system in accordance with the embodiment of FIG. 4 is a flow chart illustrating a method of operating an internal combustion engine according to the present disclosure. FIG. 5 is a schematic diagram of one embodiment of a valve actuation system according to the present disclosure, according to a variation of the valve actuation system shown in FIG. FIG. 16 is a side view of one embodiment of a valve actuation system in accordance with the embodiment of FIG. FIG. 17 is a side cross-sectional view of the embodiment according to FIG. 16. FIG. 18 is a cross-sectional side view of the LM+ feature of FIG. 17 shown in greater detail.

4 generally illustrates a valve actuation system 400 according to the present disclosure. In particular, the valve actuation system 400 includes a valve actuation motion source 402 that serves as a sole source of valve actuation motion (i.e., valve opening and closing motion) to one or more engine valves 404 via a valve actuation load path 406. The one or more engine valves 404 are associated with cylinders 405 of an internal combustion engine. As is known in the art, each cylinder 405 typically has at least one valve actuation motion source 402 uniquely associated therewith for actuation of the corresponding engine valve 404. Additionally, although only a single cylinder 405 is illustrated in FIG. 4, it will be understood that an internal combustion engine can have, and often does, more than one cylinder, and the valve actuation system described herein is applicable to any number of cylinders for a given internal combustion engine.

The valve actuation motion source 402 may comprise any combination of known elements capable of providing valve actuation motion, such as cams. The valve actuation motion source 110 may be dedicated to providing exhaust motion, intake motion, auxiliary motion, or a combination of exhaust or intake motion along with auxiliary motion. For example, in a currently preferred embodiment, the valve actuation motion source 402 may comprise a single cam configured to provide a main valve actuation motion (exhaust or intake) and at least one auxiliary valve actuation motion. As a further example, if the main valve actuation motion comprises a main exhaust valve actuation motion, the at least one auxiliary valve actuation motion may comprise an EEVO valve event and/or a compression-release engine brake valve event. As yet another example, if the main valve actuation motion comprises a main intake valve actuation motion, the at least one auxiliary valve actuation motion may comprise a late intake valve closing (LIVC) valve event. Still other types of auxiliary valve actuation motions that may be combined on a single cam with a main valve actuation motion may be known to those skilled in the art, and the present disclosure is not limited in this respect.

The valve actuation load path 406 is deployed between the valve actuation motion source 402 and at least one engine valve 404 and includes any one or more components used to transfer motion provided by the valve actuation motion source 402 to the at least one engine valve 404, such as a tappet, push rod, rocker arm, valve bridge, automatic lash adjuster, etc. Additionally, as shown, the valve actuation load path 406 also includes a lost motion adding (LM+) mechanism 408 and a lost motion subtracting (LM-) mechanism 410. As used herein, an LM+ mechanism is a mechanism in a default or "normal" state (i.e., when no control input is asserted) in which the mechanism does not transfer auxiliary valve actuation motion applied thereto and may or may not transfer any primary valve actuation motion applied thereto. On the other hand, when an LM+ mechanism is in an actuated state (i.e., when the control input is asserted), the mechanism transmits any auxiliary valve actuation motion applied to it and also transmits any main valve actuation motion applied to it. Furthermore, as used herein, an LM- mechanism is a mechanism in a default or "normal" state (i.e., when the control input is not asserted) in which the mechanism transmits the main valve actuation motion applied to it and may or may not transmit any auxiliary valve actuation motion applied to it. On the other hand, when an LM- mechanism is in an actuated state (i.e., when the control input is asserted), the mechanism does not transmit any valve actuation motion applied to it, whether main valve actuation motion or auxiliary valve actuation motion. In short, an LM+ mechanism, when actuated, can add or include valve actuation motion associated with a default or normal operating state, while an LM- mechanism, when actuated, can subtract or lose valve actuation motion associated with a default or normal operating state.

Various types of lost motion mechanisms that can function as LM+ or LM- mechanisms are known in the art, including hydraulic or mechanically based lost motion mechanisms that can be hydraulically, pneumatically, or electromagnetically actuated. For example, the lost motion mechanism depicted in FIG. 1 and taught in U.S. Pat. No. 9,790,824 (incorporated herein by this reference) is an example of a hydraulically controlled mechanically locked LM- mechanism. As described above, when there is no hydraulic oil input to the inner plunger 160 (i.e., in a default state), the locking element 180 is received in the outer recess 772, thereby "locking" the outer plunger 120 to the body 120 so that actuating motion applied thereto is transmitted. On the other hand, when an input of hydraulic oil is provided to the inner plunger 160 (i.e., in an actuated state), the locking element 180 can be retracted, thereby "unlocking" the outer plunger 120 from the body 120 so that actuating motion applied thereto is not transmitted or lost. As another example, the lost motion mechanism shown in FIG. 2 and taught in U.S. Pat. No. 6,450,144 (hereby incorporated by reference) is an example of a hydraulically controlled, hydraulically based LM+ mechanism. As noted above, in the absence of hydraulic fluid input to passages 231, 236 (i.e., in the default state), actuator piston 210 reciprocates freely within its bore, such that actuation motion that is less than the maximum distance actuator piston 210 can retract within its bore (actuator piston stroke length) is not transferred or lost, while any actuation motion applied thereto that is greater than the actuator piston stroke length is transferred.

As further depicted in FIG. 4, an engine controller 420 may be provided and operably connected to the LM+ and LM- mechanisms 408, 410. The engine controller 420 may comprise any electronic, mechanical, hydraulic, electro-hydraulic, or other type of control device for controlling the operation of the LM+ and LM- mechanisms 408, 410, i.e., for switching between their respective default and activated operating states as described above. For example, the engine controller 420 may be implemented by a microprocessor and corresponding memory that stores executable instructions used to implement the necessary control functions, including those described below, as known in the art. It is understood that other functionally equivalent implementations of the engine controller 130, such as suitable programmed application specific integrated circuits (ASICs), may equally be used. Additionally, the engine controller 420 may include peripheral devices intermediate the engine controller 420 and the LM+ and LM- mechanisms 408, 410 that enable the engine controller 420 to achieve control over the operating states of the LM+ and LM- mechanisms 408, 410. For example, if the LM+ and LM- mechanisms 408, 410 are both hydraulically controlled mechanisms (i.e., responsive to the absence or application of hydraulic fluid to the input), they may include suitable solenoids as are known in the art.

In the system 400 illustrated in FIG. 4, the LM+ mechanism 408 is disposed closer to the source of valve actuation motion along the valve actuation load path 406 than the LM- mechanism 410. Examples of such systems are described in more detail below with reference to FIGS. 6-12. However, this is not a requirement. For example, FIGS. 5 and 15 illustrate valve actuation systems 400', 1500 in which the LM- mechanisms 410, 410' are disposed closer to the source of valve actuation motion 402 than the LM+ mechanisms 408, 408', as compared to FIG. 4, although like reference numbers refer to like elements. An example of the system of FIG. 5 is described in more detail below with reference to FIGS. 12 and 13, and an example of the system of FIG. 15 is described in more detail below with reference to FIGS. 16-18.

4, the LM+ mechanism 408 is in series along the valve actuation load path 406 with the LM- mechanism 410 in all operating states of the LM+ mechanism 408. That is, as noted above, any primary valve actuation motion provided by the valve actuation motion source 402 is transferred by the LM+ mechanism 408 to the LM- mechanism 410, regardless of whether the LM+ mechanism 408 is in its default state or its actuated state. However, this is also not a requirement, as illustrated in FIG. 5, where the LM+ mechanism 408 is illustrated either in series or not in series with the LM- mechanism 410 as a function of the operating state of the LM+ mechanism 408. In this case, when the LM+ mechanism 408 is in its default operating state, i.e., when it is controlled to lose any auxiliary valve actuation motion applied to it, the LM+ mechanism 408 plays no role in transmitting the main valve actuation motion transmitted by the LM- mechanism 410, which is illustrated by the solid arrow between the LM- mechanism 410 and the engine valve 404. Effectively, in this state, the LM+ mechanism 408 is removed from the valve actuation load path 406 as depicted in FIG. 5. On the other hand, when the LM+ mechanism 408 is in its active operating state, i.e., when it is controlled to transmit any auxiliary valve actuation motion applied to it, the LM+ mechanism 408 participates in transmitting both the main and auxiliary valve actuation motions received from the LM- mechanism 410, thereby effectively placing the LM+ mechanism 408 in series, which is illustrated by the dashed arrows between the LM- mechanism 410 and the LM+ mechanism 408, and between the LM+ mechanism 408 and the engine valve 404.

The valve actuation system 400, 400' of FIG. 4 and FIG. 5 facilitates operation of the cylinder 405, and thus the internal combustion engine in a positive power mode, a deactivation mode, or an assist mode, in a system having a single valve actuation motion source 402, providing all valve actuation motion to the engine valve 404. This is further described with reference to the method illustrated in FIG. 14. In block 1402, as described above, the LM+ and LM- mechanisms are disposed in the valve actuation load path. In particular, the LM- mechanism is configured to transmit at least a main valve actuation motion applied thereto in a first default operating state, and is configured to lose the main and auxiliary valve actuation motions applied thereto in the first operating state. Additionally, the LM+ mechanism is configured to lose any auxiliary valve actuation motion applied thereto in a second default operating state, and is configured to transmit the auxiliary valve actuation motion in a second operating state, and the LM+ mechanism is in series with the LM- mechanism in the valve actuation load path during at least the second operating state.

After preparing the valve actuation system in step 1402, processing proceeds to one of blocks 1406-1410 where the engine is operated in a positive power mode, a rest mode, or an assist mode, based on controlling the operating states of the LM+ and LM- mechanisms, respectively. Thus, in block 1406, to operate the engine in a positive power mode, the LM- mechanism is placed in its first default operating state, and the LM+ mechanism is placed in its second default operating state. In this mode, the LM+ mechanism does not transmit any auxiliary valve actuation motion, but can transmit any main valve actuation motion transmitted by the LM- mechanism (depending on whether the LM+ mechanism is arranged as in FIG. 4 or FIG. 5). The net effect of this configuration is that only the main valve actuation motion is transmitted to the engine valves, as required for positive power operation.

In block 1408, to operate the engine in the pause mode, the LM- mechanism is placed in its first active operating state and the lost motion addition mechanism is in its second default operating state. In this mode, the LM- mechanism does not transmit any valve actuation motion applied to it. As a result, the corresponding cylinder is paused unless valve actuation motion is transmitted to the engine valve. Given this operation of the LM- mechanism, the operating state of the LM+ mechanism will not affect the engine valve. However, in the currently preferred embodiment, during pause mode operation, the LM+ mechanism is placed in its second default operating state.

At block 1410, to operate the engine in an assist mode, the LM- mechanism is placed in its first default operating state and the LM+ mechanism is placed in its second activated operating state. In this mode, the LM+ mechanism transmits any auxiliary valve actuation motion and any main valve actuation motion transmitted by the LM- mechanism. The net effect of this configuration is that both the main and auxiliary valve actuation motions are transmitted to the engine valves, thereby providing the auxiliary motion provided by the particular auxiliary valve actuation motion, e.g., EEVO, LIVC, compression-release engine braking, etc.

Operation of the engine during any of the various modes provided in steps 1406-1410 may continue as long as the engine is running, as illustrated by block 1412.

FIG. 6 illustrates a partial cross-sectional view of a valve actuation system 600 according to the embodiment of FIG. 4. In particular, the system 600 includes a valve actuation motion source 602 in the form of a cam operably connected to a rocker arm 604 at a motion receiving end 606 of the rocker arm 604. A rocker arm biasing element 620 (e.g., a spring) reacting against a fixed surface 622 may be provided to assist in biasing the rocker arm 604 into contact with the valve actuation motion source 602. As is known in the art, the rocker arm 604 rotatably reciprocates about a rocker shaft (not shown), thereby imparting a valve actuation motion provided by the valve actuation motion source to a valve bridge 610 via a motion imparting end 608 of the rocker arm 604. The valve bridge 610 is in turn operably connected to a pair of engine valves 612, 614. As further shown, the valve bridge 610 includes an LM- mechanism 616 (locking piston) of the type illustrated and described in FIG. 1 above, while the rocker arm 604 includes an LM+ mechanism 618 (actuator) of a type substantially similar to that illustrated and described above in connection with FIG. 2.

Details of the LM+ mechanism 618 are further illustrated in FIG. 7 along with other components disposed within the rocker arm 604. The LM+ mechanism 618 comprises an actuator piston 702 mounted on a retainer 703 such that the actuator piston 702 is slidably disposed on a lash adjustment screw 704. Further details of the LM+ mechanism 618 are described with reference to FIG. 9 below. As best shown in FIG. 9, the lash adjustment screw 704 is threadedly fastened within the actuator piston bore 710 such that the LM+ mechanism 618 is disposed in a lower portion of the actuator piston bore 710. A lock nut 704 is provided to secure the lash adjustment screw 704 at a desired lash setting during use.

FIG. 7 also illustrates a reset assembly 712 disposed within a reset assembly bore 724 that includes openings on the top and bottom (not shown) of the rocker arm 604. The reset assembly 712 includes a reset piston 714 slidably disposed within the reset assembly bore 724. A reset piston spring 715 is disposed over the reset piston 714, and a lower end of the reset piston spring 716 is secured to the reset piston 714 using a c-clip 718 or other suitable component. A washer 720 is disposed on an upper end of the reset piston spring 716. The reset assembly 712 is maintained within the reset assembly bore 724 by a spring clip 722, as known in the art. As will be described in more detail below with respect to FIGS. 10 and 11, the reset piston spring 716 biases the reset piston 714 out of the lower opening of the reset assembly bore 724 so that the reset piston 714 can contact a fixed surface (not shown in FIG. 7). As the rocker arm 604 reciprocates, the reset piston 714 slides within the reset assembly bore 724 in a controllable manner defined by the rotation of the rocker arm 604. In particular, as described in more detail below, at a desired position of the rocker arm 604, the reset piston 714 can be configured such that an annular channel 715 formed in the reset piston aligns with a reset passage 802 (FIG. 8) to effect a reset of the LM+ mechanism 618.

7 further illustrates an upper hydraulic passage 730 formed in the rocker arm 604 that receives a check valve 732. As described in more detail below, the upper hydraulic passage 730 provides hydraulic fluid (provided by suitable supply passages formed in the rocker shaft, not shown) to the actuator piston bore 710 to control the operation of the LM+ mechanism 618. A threaded plug 734 or similar device can be used to ensure a fluid-tight seal on the upper hydraulic passage 730 after installation of the check valve 732. Additionally, for completeness, FIG. 7 also illustrates a rocker arm bushing 740 that can be inserted into the rocker shaft opening 742 and onto the rocker shaft, as known in the art. Additionally, a cam follower 744 can be attached to a cam follower shaft 746 disposed in a suitable opening 748.

However, unlike the actuator piston 210 of FIG. 2, as best illustrated in FIG. 9, the actuator piston 702 of the LM+ mechanism 618 includes hydraulic passages 904, 906 that allow hydraulic fluid to be supplied to the LM- mechanism 616 through the actuator piston 702. As shown in FIG. 9, a lower hydraulic passage 908 formed in the rocker arm 604 receives hydraulic fluid from a supply channel in the rocker shaft (not shown) and routes the hydraulic fluid to a lower portion of the actuator piston bore 710. The actuator piston 702 includes an annular channel 910 formed in its sidewall surface that aligns with the hydraulic supply passage 908 throughout the stroke of the actuator piston 702. The annular channel 910 then communicates with the horizontal passage 904 and the vertical passage 906 formed in the actuator piston 702. The vertical passage 906 directs hydraulic fluid to the swivel 706, which has an opening formed therein for passing hydraulic fluid to the LM- mechanism 616. In this way, hydraulic fluid can be selectively provided as a control input to the LM-mechanism 616.

As described above and further shown in FIG. 9, the LM+ mechanism 618 includes a lash adjustment screw 704 that extends into the actuator piston bore 710. An actuator piston spring 918 is disposed between the lash adjustment screw 704 and the actuator piston 702 and abuts against a lower surface of a shoulder 920 formed on the lash adjustment screw 704, thereby biasing the actuator piston 702 away from the actuator piston bore 710. In this embodiment, the actuator piston 702 is fastened via suitable threads to a retainer 703 that engages an upper surface of the lash adjustment screw shoulder 920, thereby limiting the outward stroke of the actuator piston 702, as described in more detail below.

8 and 9 further illustrate (in phantom in FIG. 9) an upper hydraulic passage 730 formed in the rocker arm 604 to selectively supply hydraulic fluid (e.g., high speed solenoid, not shown) to the actuator piston bore 710 above the actuator piston 702. (Note that in FIG. 8, the LM+ mechanism 618 and various components forming the reset assembly 712 are not shown for ease of illustration.) A check valve 732 is provided in the wide portion 730' of the upper hydraulic passage 730 to prevent backflow of hydraulic fluid from the actuator piston bore 710 into the supply passage feeding the upper hydraulic passage 730. In this manner, a high pressure chamber can be formed in the actuator piston bore 710 between the check valve 732 and the actuator piston 702 such that a locked volume of hydraulic fluid maintains the actuator piston 702 in an extended (actuated) state in the absence of a reset of the LM+ mechanism 618 as described below.

As described above in connection with FIG. 3, a valve actuation system in which a single valve actuation motion source provides both the main and auxiliary valve actuation motion may require a reset capability to avoid overextension of the engine valve during the combined auxiliary and main valve actuation motion. In the context of the embodiment illustrated in FIGS. 6-11, venting of the locked volume of hydraulic fluid and resetting of the actuator piston 702 are provided through operation of the reset assembly 712. As best shown in FIG. 8, a reset passage 802 is provided in fluid communication with that portion of the actuation piston bore 710 to form a high pressure chamber with the actuator piston 702 and the reset piston bore 804. The reset piston 714 is effectively a spool valve having an end that extends from the bottom of the rocker arm 604 under the bias of a reset piston spring 716. In the embodiment illustrated in FIGS. 10 and 11, the reset piston 714 is of sufficient length and the reset piston spring 716 has a sufficient stroke to ensure that the reset piston 714 is in continuous contact with the fixed contact surface 1002 through all positions of the rocker arm 604.

10, the rocker arm 604 is at base circle relative to the cam 602 (i.e., rotated maximally toward the cam 602). In this state, as well as at relatively low lift (e.g., below the reset height shown in FIG. 3), the annular channel 715 is not aligned with the reset passage 802 (hidden behind the upper hydraulic passage 730, as shown in FIGS. 10 and 11) such that the outer diameter of the reset piston 714 seals communication with the reset passage 802, thereby maintaining the volume of fluid trapped within the actuator piston bore 710 (if provided). As the rocker arm 604 rotates at a higher valve lift (e.g., above the reset height shown in FIG. 3), as shown in FIG. 11, the reset piston 714 pivots about its contact point with the fixed surface 1002 and slides relative to the reset piston bore 804 such that the annular channel 715 aligns with the reset passage 802, thereby allowing trapped hydraulic oil to flow through the annular channel 715 into the radial hole 1004 formed in the reset piston 714 and vent through the top of the axial passage 1006 (shown in phantom) formed in the reset piston 714. When the rocker arm 604 rotates again after the high lift event, as in FIG. 10, the reset piston 714 translates within its bore 804, again sealing the reset passage 802, thereby allowing refilling of the actuator piston bore 710.

As mentioned above, the reset assembly 712 illustrated in FIGS. 6-11 is configured to maintain constant contact with the fixed contact surface 1002. However, it will be understood that this is not a requirement. For example, the reset assembly could instead comprise a poppet-type valve that contacts the fixed surface only when the required reset height is achieved.

As previously mentioned, the rocker arm biasing element 620 may be provided to assist in biasing the rocker arm 604 into contact with the cam 602. A feature of the disclosed system 600 is that neither the rocker arm biasing element 620 nor the actuator piston spring 918 are individually configured to individually provide sufficient force to bias the rocker arm 604 into contact with the cam 602 through substantially all operating conditions. However, in this embodiment, the rocker arm biasing element 620 and the actuator piston spring 918 are selected to function in combination for this purpose through substantially all operating conditions of the rocker arm 604. For example, to help bias the rocker arm 604 toward the cam 602, the actuator piston spring 918 provides high force only during relatively low lift valve actuation motions (e.g., EEVO, LIVC, etc.), where most is needed due to potential high speed operation. If not controlled, the biasing force applied by the actuator piston spring 918 can push the actuator piston 702 against the LM-mechanism 616 with significant force. If the LM-mechanism 616 is a mechanical locking mechanism as described with reference to FIG. 1, such forces are strong enough to impede the ability of the locking element 180 to extend and retract, thereby preventing the LM-mechanism 616 from locking and unlocking. The travel limit imposed by the lash adjustment screw shoulder 920 of the actuator piston 702 prevents such excessive loads on the LM-mechanism 616, thereby maintaining the lash space normally provided in the LM-mechanism 616 and allowing the locking element 180 to freely extend/retract as needed.

Additionally, the extension of the actuator piston 702 by the actuator piston spring 918 is relatively small, yet still reduces the range stress that the outer plunger spring 146 must withstand. The actuator piston spring 918 can then be a high force, low travel spring that provides the high force required specifically for low lift, potentially high speed valve actuation motion. This burden sharing by the actuator piston spring 918 and the outer plunger spring 146 can also alleviate the need for the rocker arm biasing element 620 to provide a high preload, allowing the design of the rocker arm biasing element 620 to focus on the slower, higher lift portion for the main valve actuation motion that occurs during quiescent operation, which is a less stringent design constraint.

FIG. 12 illustrates a partial cross-sectional view of a valve actuation system 1200 according to the embodiment of FIG. 5. In this system 600, the valve actuation motion source comprises a cam (not shown) operably connected to a motion receiving end 1206 of a rocker arm 1204 via a push tube 1202 and an intervening LM-mechanism 1216 of the type illustrated and described in FIG. 1 above. As in the embodiment illustrated in FIGS. 6-11, the rocker arm 1204 reciprocates rotationally about a rocker shaft (not shown), thereby imparting a valve actuation motion provided by the valve actuation motion source to a valve bridge 1210 via a motion imparting end 1208 of the rocker arm 1204. The valve bridge 1210 is in turn operably connected to a pair of engine valves 1212, 1214. As further shown, the rocker arm 1204 comprises an LM+ mechanism 1218 of a type substantially similar to that illustrated and described in connection with FIG. 2. In this case, hydraulic fluid is provided to the LM- mechanism 1216 via suitable passages formed in the rocker shaft and rocker arm 1204 and ball joint 1220. Similarly, hydraulic fluid is provided to the LM+ mechanism 1218 via suitable passages formed in the rocker shaft and rocker arm 1204. However, in this implementation, the check valve 732 of the previous embodiment is replaced by a control valve 1222 to establish the hydraulic lock necessary to maintain the actuator piston in an extended state. The embodiment of FIG. 12 is further characterized by the arrangement of the LM+ mechanism 1218 interacting with only a single engine valve 1214 via a suitable bridge pin 1224.

In this embodiment, the LM-mechanism 1216 includes a relatively strong spring to bias the outer plunger of the locking mechanism outward against the push rod 1202 such that the push rod 1202 is biased into contact with the cam and the rocker arm is biased toward the engine valves 1212, 1214. In this implementation, the outer plunger of the LM-mechanism 1216 is not limited during engine operation (as opposed to engine assembly), but imposing a travel limit on the LM-mechanism 1216 facilitates assembly.

Considering the configuration of the LM+ mechanism 1218, particularly the inwardly sprung actuator piston, a gap is provided between the actuator piston and the bridge pin when the LM+ mechanism 1218 is in its default state. As a result, during this default state, the LM+ mechanism 1218 is not in series along the motion load path with the LM- mechanism 1216, as described above in connection with FIG. 5. Furthermore, despite the existence of a gap during the default state, the actuator piston cannot fully extend, considering the strength of the outer plunger piston spring as described above. In this case, the actuator piston cannot fully extend until a primary motion valve event occurs, thereby creating a sufficient gap between the actuator piston and the bridge pin 1224 to allow for full extension. However, when in the extended (actuated) state, the actuator piston not only transmits the auxiliary valve actuation motion applied to it, but also the primary valve actuation motion applied to its corresponding engine valve 1214. In this case, the LM+ mechanism 1218 is placed in series with the LM- mechanism 1216 during the actuated state of the actuator piston, as described above in connection with FIG. 5.

Figure 13 illustrates a partial cross-sectional view of a valve actuation system 1300 according to the embodiment of Figure 5. In particular, the embodiment illustrated in Figure 13 is substantially identical to the embodiment of Figure 12, except that the spherical joint 1220 is replaced with an outwardly biased, limited travel slide pin 1320. In this case, the outer plunger spring of the LM-mechanism 1216 is preferably designed with a low preload during zero or low valve lift (e.g., on the base circle) and has the spring velocity required to obtain a peak force to control the full range of motion of the rocker arm 1204 over the main valve actuation motion during pause mode operation.

On the other hand, the slide pin spring 1322 used to bias the slide pin 1320 outward is configured with a relatively high preload and short stroke (substantially similar to the actuator piston spring 918 discussed above). As the slide piston 1320 is able to slide within its bore, it includes an annular channel 1334 and radial openings 1336 aligned therewith to ensure continuous fluid communication between the rocker arm 1204 and the LM-mechanism 1216 by aligning the annular channel 1334 with the fluid supply passage throughout the entire stroke of the slide piston 1320. Additionally, the stroke adjustment screw 1338 functions to limit the movement of the slide pin 1320 from its bore towards the LM-mechanism 1216. As discussed with respect to the travel limiting capability applied to the actuator piston 702 above, the stroke adjustment screw 1338 prevents the full force of the slide pin spring 1322 from being applied to the LM-mechanism 1216, which could otherwise be overloaded and interfere with its operation. By properly selecting the stroke provided by the stroke adjustment screw 1338, i.e., equal to the motion that must be lost by the LM+ mechanism during its default operating state, the lash provided to the locking element in the LM- mechanism 1216 can be selected to ensure its proper operation as described above. In effect, the assembly of the slide pin 1320, slide pin spring 1322 and stroke adjustment screw 1338 constitute part of the LM+ mechanism in this embodiment.

As noted above, various specific combinations of outward (extended) and inward springing (retracted) elements in the LM+ and LM- mechanisms may be provided, with travel limiting as needed. More generally, in one implementation, the LM- mechanism (more specifically, an element or component thereof) may be biased to an extended position, and the LM+ mechanism (again, more specifically, an element or component thereof) may be biased to a retracted position. In this case, the extended position of the LM- mechanism may be travel limited. In another implementation of any given embodiment, the LM- mechanism may be biased to an extended position by a first force, and the LM+ mechanism may also be biased to an extended position by a second force. In this case, the first biasing force is preferably greater than the second biasing force. Additionally, again, the extended position of the LM- mechanism may be travel limited. In yet another implementation, the LM- mechanism may be biased to an extended position, and the LM+ mechanism may also be biased to an extended position. In this case, however, the extended position of the LM+ mechanism is limited in travel. In this implementation, a possible advantage of limiting the travel of the LM+ mechanism is to allow zero load on the valve train on the cam base circle to reduce bushing wear.

4, and as shown with respect to FIG. 15, in which like reference numbers refer to like elements as compared to FIG. 4, a system 1500 can be provided in which the LM-mechanism 410' is disposed closer to the valve actuation motion source 402 along the valve actuation motion path 406 than the LM-mechanism 408'. However, unlike the system 400' of FIG. 5, the LM+ mechanism 408' shown in FIG. 15 is always in series with the LM-mechanism 410', regardless of the operating state (default or activated) of the LM+ mechanism 408', and thus the LM+ mechanism 408' always serves to transmit the main valve actuation motion transmitted by the LM-mechanism 410' and is never removed from the valve actuation load path 406.

In particular, when the LM+ mechanism 408' is in its default operating state, the LM+ mechanism 408' loses any auxiliary valve actuation motion, but is configured to transmit the main valve actuation motion applied thereto by the valve actuation motion source 402 and the LM- mechanism 408'. On the other hand, when the LM+ mechanism 408' is in its active operating state, i.e., when it is controlled to transmit any auxiliary valve actuation motion applied thereto, the LM+ mechanism 408' participates in transmitting both the main and auxiliary valve actuation motions received from the valve actuation source 402 and the LM- mechanism 410'. So configured, the valve actuation system 1500 facilitates operation of the cylinder 405, and thus the internal combustion engine in a positive power mode, a deactivation mode, or an auxiliary mode (e.g., engine braking) in a system having a single valve actuation motion source 102, providing all valve actuation motion to the engine valve 404. That is, the system 1500 can implement the method shown with reference to FIG. 14 and described above. In this case, however, the provisioning of the LM- and LM+ mechanisms in block 1402 occurs in the pre-rocker valve train components and the valve bridge, respectively, as described in more detail below.

16-18 illustrate a valve actuation system 1600 according to the embodiment of FIG. 15. In this embodiment, the valve actuation system 1600 includes an LM- mechanism 1602 disposed in or on a pre-rocker arm valve train component and an LM+ mechanism 1604 disposed in a valve bridge. As used herein, a pre-rocker arm valve train component may include any valve train component disposed in the valve train between a valve actuation motion source (e.g., a cam, not shown) and a rocker arm 1620. For example, this may include devices known in the art, such as push rods, tappets, roller followers, etc. In the example shown in FIGS. 16 and 17, the pre-rocker arm valve train component includes a push rod 1610 operably connected to a roller follower 1612 to establish contact between the push rod 1610 and a cam (not shown). In this embodiment, the LM-mechanism 1602 is attached to the upper end of the push rod 1610 such that the LM-mechanism 1602 is operatively connected to both the push rod 1610 and the rocker arm 1620. Further in this example, the rocker arm 1620 is mounted for reciprocating motion on a rocker shaft (not shown). The rocker arm 1620 is then operatively connected to a valve bridge 1630 in which the LM+ mechanism 1604 is disposed. As in a conventional internal combustion engine, the valve bridge 1630 is operatively connected to two or more engine valves 1642, 1644 (intake or exhaust valves) that are biased to a closed position by corresponding valve springs 1646, 1648. FIG. 16 further illustrates a fixed reaction surface 1650 that contacts the upper end of the LM-mechanism 1602, as described in more detail below.

17 and 18, further details of the embodiment of FIG. 16 are shown and described. As mentioned above, the push rod 1610 is attached to the LM-mechanism 1602. In this embodiment, the LM-mechanism 1602 comprises a housing 1702 attached to the push rod 1610 by an interference fit or threaded engagement between a stud 1704 extending away from a base wall 1703 of the housing 1702 and an inner diameter 1705 of the push rod 1610. Alternatively, the housing 1702 may be integrally formed as part of the push rod 1610, or the push rod 1610 may be inserted into a receptacle formed on the exterior of the base wall 1703 of the housing 1702. A closed housing bore 1706 is formed in the housing 1702 and is configured to receive an outer plunger 1708, an inner plunger 1712, an inner plunger spring retainer 1714, an inner plunger spring 1716, an outer plunger spring 1709, and one or more locking elements 1718, shown in this embodiment as wedges. The outer plunger spring 1709, disposed within the housing bore 1706 between the base wall 1703 and the outer plunger 1708, biases the outer plunger 1708 upwardly within the housing bore 1706 (as shown in FIG. 17 ). The inner plunger 1712 is disposed within an inner bore 1710 formed in the outer plunger 1708. An inner plunger spring 1716 disposed between the inner plunger spring retainer 1714 (secured to close the lower end of the inner bore 1710) and the inner plunger 1712 biases the inner plunger 1712 upwardly within the inner bore 1710. The upward movement of the inner plunger 1712 is limited by a stop surface 1726 formed at the upper end of the inner bore 1710. The outer plunger 1708 includes an opening extending through a sidewall of the outer plunger 1708 in which a wedge 1718 is disposed, the wedge 1718 being configured to engage an annular outer recess 1720 formed in a surface defining the housing bore 1706.

In the absence of hydraulic control applied to the inner plunger 1712 through the opening at the top end of the inner bore 1710, i.e., in the default state of the LM-mechanism 1602 as shown in FIG. 17, the inner piston spring 1716 biases the inner plunger 1712 into a predetermined position such that the wedge 1718 extends from an opening formed in the outer plunger 1708, thereby engaging the outer recess 1720 and effectively locking the outer plunger 1708 in position relative to the housing 1702. In this default state, any valve actuation motion (whether primary or secondary) applied to the push tube 1610 is transmitted by the LM-mechanism 1602 through the outer plunger 1708, which is effectively locked in position relative to the housing 1702. However, providing sufficient pressurized hydraulic fluid to the top of the inner plunger 1712 causes the inner plunger 1712 to slide downward, thereby allowing the wedge 1718 to retract and disengage from the outer recess 1720, thereby effectively unlocking the outer plunger 1708 relative to the housing 1702 and allowing the outer plunger 1708 to slide freely within the housing bore 1706 under the bias provided by the outer plunger spring 1709. In this operating state, any valve actuation motion applied to the housing 1702 by the push rod 1610 reciprocates the push rod 1610 and the housing 1702 according to the applied actuation motion while the outer plunger 1708 remains stationary. In this manner, assuming the movement of the outer plunger 1708 within the housing bore 1706 is greater than the maximum range of the applied valve actuation motion, such valve actuation motion is not transmitted to the engine valve and is effectively lost such that the corresponding cylinder is deactivated.

Further, in the illustrated embodiment, the bias spring 1722 is disposed in contact between a flange 1724 formed on and extending radially from the outer surface of the housing 1702 and a fixed contact surface 1650. As shown, the fixed contact surface 1650 is configured to allow the outer plunger 1708 to contact a lash adjustment screw 1730 disposed on the rocker arm 1620 while still engaging the upper end of the bias spring 1722. The bias spring 1722 is provided to manage the inertia of the push rod 1610 and the LM-mechanism 1602 as they reciprocate in accordance with a valve actuation motion applied to the push rod 1610 and ensure that the push rod 1610 maintains contact with the source of valve actuation motion (in this example via the roller follower 1612). The use of fixed contact surface 1650 for this purpose prevents the relatively large bias applied by bias spring 1722 from also being applied (through rocker arm 1620) to LM+ mechanism 1604 and interfering with its operation. In comparison, outer plunger spring 1709 is a relatively light spring that is strong enough to bias outer plunger 1708 into contact with rocker arm 1620/lash adjustment screw 1730, but is also not strong enough to interfering with operation of LM+ mechanism 1604.

As known in the art, the rocker shaft (not shown) may be provided with channels for supplying pressurized hydraulic fluid to hydraulic passages 1736, 1738 formed in the rocker arm 1620. As further known in the art, the supply of such hydraulic fluid may be controlled through the use of appropriate solenoids (not shown) under the supervision of the controller 420. The hydraulic passages 1736, 1738 route hydraulic fluid to the LM- mechanism 1602 and the LM+ mechanism 1604, respectively. By selectively controlling the flow of hydraulic fluid through the respective passages 1736, 1738, the default/operating state of each of the LM- and LM+ mechanisms 1602, 1604 may likewise be controlled.

To this end, the rocker arm 1620 includes a lash adjustment screw 1730, as known in the art, having a first fluid passage 1734 formed therein and terminating at a ball joint 1732. The ball joint 1732 is formed to engage a complementarily configured upper surface of the outer plunger 1708 such that fluid communication between the first fluid passage 1734 and the inner bore 1710 is provided throughout the entire operation of the valve actuation system 1600. A first hydraulic passage 1736 is in fluid communication with the first fluid passage 1734, and hydraulic fluid may be selectively provided as a control input to the LM-mechanism 1602 as described above.

Similarly, the rocker arm 1620, in this example, includes a ball joint 1742 having a second fluid passage 1740 formed therein that is in communication with the second hydraulic passage 1738. The ball joint 1742 is coupled to a pivot or e-foot 1744 having an opening 1746 formed therein such that continuous fluid communication is provided between the first fluid passage 1740 and the LM+ mechanism 1604. Again, this continuous fluid communication allows hydraulic fluid to be selectively supplied as a control input to the LM+ mechanism 1604, as described above.

Further details of the LM+ mechanism 1604 are described with reference to FIG. 18 below. In particular, the LM+ mechanism 1604 comprises a lost motion piston 1802 disposed within a closed centrally formed bore 1804 in the valve bridge 1630. The lost motion piston 1802 comprises a piston opening 1803 providing fluid communication between the first fluid passageway 1740/opening 1746 and an internal bore 1813 formed within the lost motion piston 1802. The lost motion piston 1802 further comprises a check valve assembly comprising a check disk (or ball) 1802, a check spring 1808, a check spring retainer 1810, and a retainer clip 1812 disposed within the bore 1813. The retainer clip 1812 maintains the check spring retainer 1810 in a fixed position within the bore 1813 such that the check spring 1808 continuously biases the check disk 1806 into contact with the top wall of the lost motion piston 1802, thereby sealing the first fluid passageway 1740 from the bore 1813 in the absence of sufficient pressurized hydraulic fluid provided from the first fluid passageway 1740. The lost motion piston 1802 is biased from the bore 1804 into contact with the orbit 1744 by a piston spring 1814 disposed within the bore 1804, thereby ensuring continuous contact, and therefore continuous fluid communication, between the lost motion piston 1802 and the orbit 1744.

As known in the art, the lost motion piston 1802 is configured to move a distance (lost motion lash) at least as large as any auxiliary valve actuation motion applied by the rocker arm 1620. Thus, when hydraulic fluid is not supplied to the lost motion piston 1802 and its check valve assembly, the lost motion piston 1802 bottoms out in the bore 1804 under the influence of a bias applied to the rocker arm 1620 by the outer plunger spring 1709 via the outer plunger 1708, and remains bottomed out in the bore 1804 when valve actuation motion is applied to the lost motion piston 1802. Because the amount of travel of the lost motion piston 1802 is at least as large as any auxiliary valve actuation motion applied to it, such auxiliary valve actuation motion is lost in this situation, but larger valve actuation motion, such as primary event valve actuation, is transferred to the valve bridge 1630 via the lost motion piston 1802.

However, when sufficient pressurized hydraulic fluid is supplied to the lost motion piston 1802 through the check valve assembly, the hydraulic fluid passes through the check disk 1806 and into the bore 1804 below the lost motion piston 1802. As is known in the art, this establishes a locked volume of relatively incompressible hydraulic fluid behind the lost motion piston 1802, thereby causing the lost motion piston 1802 to extend from its bore 1804 and remain extended while valve actuation motion is applied to it. As a result, all valve actuation motion (both primary and auxiliary valve actuation motion) applied to the lost motion piston 1802 is transferred to the valve bridge 1630.

As mentioned above, the embodiment shown in Figures 16-18 is based on the use of a pushrod as a pre-rocker arm valve train component configured to include an LM-mechanism. However, as further described above, the pre-rocker arm valve train component may be implemented using other valve train components. For example, in one embodiment, an LM-mechanism such as the locking mechanism described above may be implemented in a cam follower, lifter, or similar component. In this case, the hydraulic fluid required to control the locking mechanism may be supplied through suitable passages formed in the pushrod or using other hydraulic fluid supply techniques known to those skilled in the art.

Claims (11)

1. A valve actuation system for use in an internal combustion engine including a cylinder, at least one engine valve associated with the cylinder, and a valve actuation load path including a valve bridge operatively connected to a rocker arm and a pre-rocker arm valve train component operatively connected to the rocker arm, the valve actuation system comprising:
a single cam configured to provide a primary valve actuation motion and an auxiliary valve actuation motion to actuate the at least one engine valve through the valve actuation load path;
a lost motion subtraction mechanism disposed on the pre-rocker arm valve train component and configured to transfer at least the primary valve actuation motion in a first default operating condition and configured to lose the primary valve actuation motion and the auxiliary valve actuation motion in a first operating condition;
a lost motion adder mechanism disposed within the valve bridge and configured to lose the auxiliary valve actuation motion in a second default operating state and configured to transfer the auxiliary valve actuation motion in a second operating state, the lost motion adder mechanism disposed in series with the lost motion subtracter mechanism in the valve actuation load path;
A valve actuation system comprising: The internal combustion engine is operated by using the lost motion subtraction mechanism and the lost motion addition mechanism.
2. The valve actuation system of claim 1, further comprising an engine controller configured to operate the valve actuation system in a positive power mode in which the lost motion subtraction mechanism is in the first default operating state and the lost motion adder mechanism is in the second default operating state ; a pause mode in which the lost motion subtraction mechanism is in the first operating state and the lost motion adder mechanism is in the second default operating state; or an assist mode in which the lost motion subtraction mechanism is in the first default operating state and the lost motion adder mechanism is in the second operating state. the auxiliary valve actuation motion comprising:
The valve actuation system of claim 1 , wherein the valve actuation system comprises at least one of an early exhaust valve opening valve actuation motion, a late intake valve closing valve actuation motion, or an engine braking valve actuation motion. The valve actuation system of claim 1, wherein the lost motion subtraction mechanism is a hydraulically controlled mechanical locking mechanism. The valve actuation system of claim 1, wherein the lost motion compensation mechanism is a hydraulically controlled actuator. The valve actuation system of claim 5, wherein the lost motion adder mechanism further includes a hydraulically controlled check valve that supplies hydraulic fluid to the hydraulically controlled actuator. 2. The valve actuation system of claim 1, further comprising a first spring configured to bias the pre-rocker arm valve train component toward the single cam. 8. The valvetrain actuation system of claim 7, wherein the pre-rocker arm valvetrain component includes a push rod, and the first spring is operatively connected to the push rod. The valve actuation system of claim 1, further comprising a second spring configured to bias the rocker arm toward the single cam. 10. The valve actuation system of claim 9 , wherein the second spring is disposed within the lost motion adder mechanism. 1. A method of operating an internal combustion engine including a cylinder and at least one engine valve associated with the cylinder, further including a single cam configured to provide primary and auxiliary valve actuation motions to actuate the at least one engine valve through a valve actuation load path including a valve bridge operatively connected to a rocker arm and a pre-rocker arm valve train component operatively connected to the rocker arm, the method comprising:
providing a lost motion subtraction mechanism disposed on the pre-rocker arm valve train component, the lost motion subtraction mechanism configured to transmit at least the primary valve actuation motion in a first default operating condition, and configured to lose the primary valve actuation motion and the auxiliary valve actuation motion in a first operating condition;
providing a lost motion adder mechanism disposed within the valve bridge, the lost motion adder mechanism configured to lose the auxiliary valve actuation motion in a second default operating state and configured to transfer the auxiliary valve actuation motion in a second operating state, the lost motion adder mechanism disposed in series with the lost motion subtraction mechanism in the valve actuation load path;
The method further includes operating the internal combustion engine in a positive power mode in which the lost motion subtraction mechanism is in the first default operating state and the lost motion adder mechanism is in the second default operating state ; or a sleep mode in which the lost motion subtraction mechanism is in the first operating state and the lost motion adder mechanism is in the second default operating state; or an assist mode in which the lost motion subtraction mechanism is in the first default operating state and the lost motion adder mechanism is in the second operating state.

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