Patent Publication Number: US-11649739-B2

Title: Valve bridge constraints and guides and related methods

Description:
FIELD 
     The instant disclosure relates generally to valve actuation systems in internal combustion engines, and in particular to valve bridge systems comprising constraints and guides for managing bridge jump and other uncontrolled valve bridge motion during engine operation. Constraints may include an e-foot collar, an extended portion having a lower guide surface on the bridge, and a bridge brake pin. Guides may include valve stem tip lead-in chamfers surrounding the valve bridge valve pockets as well as a deflection surface on the bridge extended portion. The instant disclosure also relates generally to methods of configuring valve bridges with constraints and guides. 
     BACKGROUND 
     Valve actuation systems for use in internal combustion engines are well known in the art. Such valve actuation systems typically include a valve train that, in turn, comprises one or more components that transfer valve actuation motions from a valve actuation motion source (e.g., one or more cams) to an engine valve.  FIG.  1    illustrates a typical exhaust valve actuation subsystem in a prior art valve actuation system having a lost motion valve bridge  600 / 700 . It will be understood that similar components may be used to implement actuation of intake valves. A main exhaust rocker arm  100 / 400  may be pivotally mounted and adapted to rotate about a rocker shaft  110 . A motion follower  120  may be disposed at one end of the main exhaust rocker arm  100 / 400  and may contact and follow a motion source (i.e., rotating cam  260 ) to impart motion to the rocker. The cam  260  may be controlled with a controller  265  and may include a single main exhaust bump  262  (or a main intake bump in the case of an intake valve actuation system). As is well-known in the art, hydraulic fluid may be supplied to the rocker arm  100 / 400  from a hydraulic fluid supply (not shown) under the control of a solenoid hydraulic control valve (not shown). The hydraulic fluid may flow through a passage  510  formed in the rocker shaft  110  to a hydraulic passage  215  formed within the rocker arm  100 / 400 . A return or auxiliary passage  520  may also be formed in the rocker shaft. 
     Still referring to  FIG.  1   , a swivel foot, also commonly referred to as an elephant foot or e-foot  240 , may be part of a screw assembly  230  disposed at one end of the rocker arm  100 / 400  to convey motion from the rocker arm  100 / 400  to the valve bridge  710 , which spans two or more engine valves  810 / 890  and  820 / 920  associated with a given cylinder. In many cases, such valve bridges permit another component of a valve train (e.g., a rocker arm) to simultaneously actuate the engine valves engaged with the valve bridge through a brake pin  650 / 700  disposed in a bore  714 . The position of the swivel foot  240  relative to the rocker arm  100 / 400  may be adjusted using an adjusting screw  232  secured with a threaded fastener  234  which thereby provides adjustment of lash (i.e., space between the swivel foot  240  and valve bridge  710 ). A hydraulic passage  235  in communication with the rocker passage  215  may be formed in the screw  232  to convey fluid from the rocker passage  215  to the valve bridge. The swivel foot  240  may contact the lost motion valve bridge  600 / 700 . The exhaust valve bridge  600 / 700  may include a valve bridge body  710  having a central opening  712  extending through the valve bridge and a side opening  714  extending through a first end of the valve bridge. The side opening  714  may receive a sliding pin  650  which contacts the valve stem of a first exhaust valve  810 . The valve stem of a second exhaust valve  820  may contact the other end of the exhaust valve bridge. 
     Ideally, in operation, opposition of forces applied by a motion-conveying component (such as a rocker arm) and by engine valve springs ensures that a valve bridge remains in contact (with allowances for normal lash settings) simultaneously with the motion-conveying component and with the engine valves. In this manner, the valve bridge is consistently maintained in alignment with, and positioned to convey valve actuation motions to, the engine valves. As used herein, this state of the valve bridge is referred to as a “controlled state” of the valve bridge relative to the engine valves. 
     Some valve actuation systems are configured to provide so-called auxiliary valve actuation motions, i.e., valve actuation motions other than or in addition to the valve actuation motions used to operate an engine in a positive power production mode through the combustion of fuel. In such valve actuation systems, a valve train component (e.g., tappet, pushrod, rocker arm, valve bridge, etc.) may be configured to include devices or lost motion assemblies that permit valve actuation motions to be transmitted through the valve train component to the engine valves, or selectively “lost” where such motions are not transmitted through the valve train component to the engine valves. The signal to activate or deactivate the lost motion assembly and thereby cause the lost motion assembly to absorb or convey motion may be provided via hydraulic (oil) pressure controlled by an upstream solenoid valve.  FIG.  1    illustrates an example of such a system described in U.S. Patent Application Publication No. 2012/0024260, the teachings of which are incorporated herein by this reference. In this case, a valve bridge assembly  600 / 700  is provided with a lost motion assembly in the form of a locking mechanism. The central opening  712  of the exhaust valve bridge  600  may receive a lost motion or locking assembly including an outer plunger  720  disposed in an outer plunger bore  722 , a cap  730  disposed in the outer plunger  720 , an inner plunger  760 , an inner plunger spring  744 , an outer plunger spring  746 , and one or more wedge rollers or balls  740 . The swivel foot  240  engages the cap  730  and thus conveys motion to the outer plunger  720  and ultimately to the bridge  600  and valves if the outer plunger  720  is locked relative to the bridge  600 . In the illustrated embodiment, the locking mechanism ball  740  may be located in an inner plunger recess  762  and upon upward motion of the inner plunger  760  be forced through an opening in an outer plunger  720  and into engagement with a recess  770  formed in the body of the valve bridge. In this state, the ball  740  is prevented from disengaging the recess  770  due to an outer diameter of the inner plunger  760 , thereby locking the outer plunger  720  into a fixed relationship relative to the valve bridge  710 . Consequently, any valve actuation motions applied to the outer plunger  720  by a rocker arm  100 / 400  is conveyed to the valve bridge  710  and to the engine valves  810 / 910 ,  820 / 920 . However, when a recess formed in the inner plunger  760  is aligned with ball  740 , the ball is free to disengage the recess  770  in the valve bridge  710 , thereby unlocking the outer plunger  720  and allowing it to reciprocate relative to the valve bridge  710 . In this state, any valve actuation motions applied to the outer plunger  720  cause the outer plunger to move within the valve bridge  710  and are not conveyed to the engine valves. Another valve bridge-based locking/unlocking system is disclosed in U.S. Patent Application Publication No. 2014/0326212, the teachings of which are incorporated herein by this reference. 
     However, in systems of the type illustrated in  FIG.  1   , the possibility exists for partial engagement of the locking mechanism, particularly in the operational environment when the valve bridge is reciprocating rapidly and under high loads. Partial engagement may occur, for example, where the inner plunger or latch piston in prior art systems such as those described above moves out of full engagement with the ball or wedge elements. In this case, it is possible during the rapid changing in loading and high-speed vibration of the bridge and other valve train components during engine operation for slippage of the locking mechanism. Partial engagement and slippage of the locking mechanism may occur after valve normal actuation motion (i.e., valve opening motion) is initially applied by the bridge to the engine valves. Slippage after such initial motion may result in rapid release of valve spring energy as one or both of the engine valves slam closed against their respective valve seats. When this happens, the force provided by the valve actuation components to open the engine valves is suddenly removed, permitting the engine valves to rapidly accelerate to a closed position in an unrestrained manner under the considerable force of the valve springs. When the engine valves reach the fully closed position (i.e., stopped against the valve seats formed in the cylinder head), the momentum of the valve bridge may cause the valve bridge to “jump” from the valve stem tips. That is, the valve bridge will continue movement in an uncontrolled manner and generally in a direction away from and/or out of alignment with one or both of the engine valve stems. Such motion may create potential for collision of the valve bridge with the rocker arm or other component in the valve train or engine cylinder head environment. In extreme circumstances it may be possible for the valve bridge to completely jump off of one or both of the valve stem tips and remain dislodged from the engine valves, thereby causing engine failure and/or damage. It is also known for uncontrolled states of valve bridges to occur because of overspeed operation of an internal combustion engine. This type of movement of the valve bridge—to a position in which system stability or operation is jeopardized—will be referred to herein as “uncontrolled movement” and, as used herein, this state of the valve bridge of being in a position in which system stability or operation is jeopardized is referred to as an “uncontrolled state” of the valve bridge relative to the engine valves. 
     Given the potential for valve bridge jump, misalignment and associated detrimental effects on engine and valve actuation system operation and wear in prior art systems, solutions that prevent, minimize, accommodate or guide against uncontrolled states or positions of valve bridges (regardless of the cause) would represent a welcome addition to the art. 
     SUMMARY 
     According to an aspect of the disclosure, valve bridges may include constraints and guides for controlling and managing valve bridge motion variances during engine operation. Constraints contemplated by the disclosure include an e-foot collar adapted to surround the e-foot and an extended portion on the valve bridge adapted to fit between the valve springs. Guides contemplated by the disclosure include lead-in chamfers surround the valve pockets on the valve bridge for guiding the valve tips into the valve pockets when the valve bridge becomes misaligned and a deflecting surface on the extended portion for preventing the extended portion from catching on sharp corners or other features in the valve bridge environment. The disclosed constraining and guiding features prevent bridge jump or other bridge motion that would otherwise be uncontrolled and thus maintain the valve bridge in a controlled state throughout engine operation. 
     According to an aspect, the disclosure provides a valve bridge for use with an engine valve assembly of an internal combustion engine, the engine valve assembly comprising a plurality of engine valves, the internal combustion engine having a valve train for conveying motion from a motion source to the valve bridge, the valve train including an e-foot adapted to engage the valve bridge, the valve bridge comprising a central bridge housing; a locking assembly arranged in the central bridge housing and having an e-foot engagement surface, the locking assembly adapted to selectively lock or allow movement of the e-foot engagement surface relative to the central bridge housing to thereby convey or absorb motion; and the bridge further comprising a control surface arranged to contact the e-foot when the bridge would otherwise move to an uncontrolled state, the control surface thereby maintaining the bridge in a controlled state throughout engine operation. According to a further aspect, the control surface may be defined by a collar which may be circular, and which may completely or partially surround an e-foot engagement surface on the bridge. According to a further aspect, the e-foot engagement surface may be on a plunger or piston assembly arranged in a central bridge housing. According to a further aspect, the control surface may extend a sufficient distance from the central bridge housing to constrain movement of the valve bridge relative to the e-foot to maintain the bridge in a controlled state. According to a further aspect, the control surface may extend a sufficient distance from the central bridge housing to limit movement of the valve bridge through a maximum controlled displacement. According to a further aspect, the valve bridge may comprise a valve pocket defining a valve stem seat for receiving a valve stem tip and a lead-in surface adapted to guide the valve stem seat into alignment with the valve stem tip when the bridge would otherwise move to an uncontrolled position. According to another aspect, the lead-in surface may be a chamfer. According to a further aspect, the lead-in surface may extend a sufficient distance from the valve seat to guide the valve stem seat into alignment when a maximum bridge jump displacement would otherwise occur. According to a further aspect, a extended portion having at least one lower guide surface may be disposed proximate the central bridge housing and may have at least one lower guide control surface configured to limit bridge movement by engaging a valve spring assembly, including a valve spring and a valve spring retainer, which may be oversized, to maintain the bridge in a controlled state. According to a further aspect, the valve bridge may comprise a brake pin disposed in a brake pin bore to further constrain movement of the valve bridge. Moreover, according to one aspect, the disclosed constraining e-foot collar and extended portion provide constraints on, and thus define, a worst-case deviation in bridge position and this worst-case position can be used to configure the guiding surfaces, such as the lead-in chamfers to ensure that the lead-in chamfers catch and guide the valve bridge back to an aligned and controlled position for all possible errant movements that could occur. Thus, the valve bridge is maintained in a controlled position and valve bridge jump and errant, uncontrolled motion is prevented. 
     According to one aspect, a valve bridge may include an e-foot collar with a control surface that surrounds the e-foot to thereby constrain movement (translation, pitch, roll or yaw) of the valve bridge relative to the e-foot. According to an aspect, a valve bridge for use with an engine valve assembly of an internal combustion engine, the engine valve assembly comprising a plurality of engine valves, the internal combustion engine having a valve train for conveying motion from a motion source to the valve bridge, the valve train including an e-foot adapted to engage the valve bridge, the valve bridge may comprise: a central bridge housing; a locking assembly arranged in the central bridge housing and having an e-foot engagement surface, the locking assembly adapted to selectively lock or allow movement of the e-foot engagement surface relative to the central bridge housing to thereby convey or absorb motion; and the bridge further comprising a control surface arranged to contact the e-foot when the bridge would otherwise move to an uncontrolled state, the control surface thereby maintaining the bridge in a controlled state throughout engine operation. 
     According to another aspect, a valve bridge may include an extended portion on the bridge, the extended portion defining one or more control surfaces that are arranged and adapted to engage valve springs and/or valve spring retainers when the valve bridge position deviates from a controlled state to thereby constrain movement of the valve bridge. 
     According to another aspect, a valve bridge may include valve stem tip lead-in chamfers surrounding the valve pockets. The lead-in chamfers are configured to catch the valve stem tips at all possible positions of the valve bridge relative to the valve stem tips as defined by the constraints of the e-foot collar control surface and/or the extended portion control surface. 
     According to another aspect, a bridge brake pin may provide further constraint on the bridge motion in combination with the e-foot collar constraint. This configuration may be further combined with the extended portion constraint, the valve lead-in surfaces surrounding the valve bridge valve pockets and/or a deflection surface on a bridge extended portion, each feature used alone or in combination with one or more of the other features. 
     According to another aspect, the bridge extended portion may be provided with a deflection feature for preventing the bridge extended portion from catching on sharp corners or surfaces in the overhead engine environment during engine operation. 
     According to another aspect, a process for configuring valve bridge control surfaces includes evaluating extreme positions of a valve bridge in both locked and unlocked states, configuring an e-collar to constrain bridge movement, optionally configuring an extended portion control surface to constrain bridge movement, and optionally configuring valve tip lead in chamfers based on the constraints defined by the e-collar and/or extended portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, in which: 
         FIG.  1    is a cross-sectional illustration of a valve actuation system that includes a valve bridge having a locking mechanism in accordance with prior art; 
         FIG.  2    is an illustration of a lower front perspective view of a valve bridge in accordance with the instant disclosure; 
         FIG.  3    is an illustration of an upper front perspective view of a valve bridge in accordance with the instant disclosure; 
         FIG.  4    is a bottom view of the valve bridge of  FIGS.  2  and  3   ; 
         FIG.  5    is a cross-sectional view of a valve bridge (along section line  5 - 5  in  FIG.  3   ) showing the valve bridge in a partially jumped condition; 
         FIG.  6    is an illustration of a perspective view of the valve bridge of  FIGS.  2 - 5    deployed in an internal combustion engine and in a controlled state; 
         FIG.  7    is an illustration of a perspective view of the valve bridge of  FIGS.  2 - 6    deployed in an internal combustion engine and in an uncontrolled state in which the bridge is separated from the valve tips; 
         FIGS.  8 A- 8 C  are cross-sectional illustrations of the valve bridge of  FIGS.  2 - 7    showing a sequence of a bridge jump condition or event; 
         FIG.  9    is a partial cross-sectional illustration the valve bridge (along line  9 - 9  in  FIG.  3   ) with the valve bridge at a peak jump height; 
         FIGS.  10 A- 10 D  illustrate in partial cross-section a sequence in which a valve tip lead in chamfer in accordance with the instant disclosure maintains a valve bridge in a controlled state; 
         FIG.  11    is a schematic illustration of a lead-in chamfer configuration and example bridge constraint geometry in accordance with the instant disclosure; 
         FIG.  12    illustrates a cutaway view of a braking pin and e-foot collar constraint configuration in accordance with an aspect of the instant disclosure; 
         FIG.  13    illustrates an example method or process for configuring valve bridge control surfaces in accordance with the instant disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS.  2 - 6   , a valve bridge  200  in accordance with the instant disclosure includes a guide feature in the form of a collar or vertically extending wall  202  that is adapted to interface with, and control, movement of the valve bridge  200  relative to an e-foot on the rocker arm. Referring particularly to  FIG.  6   , e-foot (also termed a swivel foot)  204  of a rocker arm  206  is adapted to engage the valve bridge  200  when the valve bridge  200  is deployed to an engine environment (i.e., installed). The collar  202  may extend upward from a main body portion  220  which may have a central bridge housing to house components of the bridge locking or collapsing mechanism  250 . The collar  202  may define a control surface  203  on an interior thereof for constraining movement of the valve bridge  200  relative to the e-foot  204 , thereby preventing uncontrolled movement of the valve bridge relative to the e-foot. Collar  202  may include one or more flattened areas on an outer surface thereof ( FIG.  6   ) to provide clearance and/or constraint of the valve bridge movement relative to other engine components in the overhead environment. Collar  202  and the control surface  203  may completely surround an e-foot engagement surface  252 , which may be disposed on a cap  254  of the locking assembly or mechanism  250  in a manner that is similar to cap  730  described in the context of  FIG.  1   . As will be recognized, variations on the continuous surface shown in this example are contemplated by the instant disclosure, for example, intermittent or discontinuous surfaces extending upward and surrounding the e-foot engagement surface. For example, the collar need not be a complete, continuous circular feature. There may be intermittent walls with slots or spaces between them, forming a number of control surfaces surrounding the e-foot. The slots or spaces may be dimensioned such that the e-foot is prevented from passing laterally through the slots or spaces. 
       FIG.  3    illustrates an isometric top front view of the example bridge  200 .  FIG.  3    also illustrates a three-dimensional reference space defined by three axes and useful for understanding bridge movement in the context of this disclosure: a longitudinal axis  10  extending through locking mechanism (center of central bridge housing) and the valve stem pockets; a lateral axis  20  extending orthogonally to the longitudinal axis  10  and through the locking mechanism; and a vertical axis  30  extending orthogonally to both the longitudinal axis  10  and the lateral axis  20 . This reference space provides a frame of reference for describing the various bridge movements that the constraining features of the instant disclosure may restrict or accommodate. As will be appreciated from this disclosure, bridge jump and the corresponding tendency of the bridge to move towards an uncontrolled state may involve one or more of translation, rotation, pitch, roll or yaw relative to one or more of these three axes. For example, bridge jump may involve translation of the valve bridge  200  upward along the vertical axis, as well as pitch of the valve bridge  200  relative to the longitudinal axis (i.e., with pitch causing one valve step pocket to elevate higher than the other valve stem pocket), as well as roll about the longitudinal axis (i.e., with roll causing rotation of the valve bridge about the longitudinal axis). In accordance with this disclosure, motion of the valve bridge may be constrained to prevent or accommodate any one or a combination of these motions to an extent that maintains the valve bridge in a controlled state, or, put another way, prevents the valve bridge from moving to what would otherwise be an uncontrolled state. 
     As shown in  FIG.  6   , the vertical extent or height of the collar  202  may be configured to provide that, during a controlled state operation of the valve bridge  200  as shown in  FIG.  6   , when the locking mechanism is locked in place and at a maximum height or stroke relative to the valve bridge main body portion  220 , the bottom surface e-foot  204  is positioned above a terminal edge  209  of control surface  203 . Such a configuration may facilitate easy installation and removal of the bridge  200 , for example. Moreover, the vertical extent or height of the collar  202  is such that, during a collapsed or unlocked state of the locking assembly or mechanism  250  included in the valve bridge  200 , the e-foot  204  may translate into the space delimited by the collar  202  and control surface  203 . The control surface  203  is also dimensioned (i.e., has sufficiently large diameter) to be free from engagement with the e-foot during normal, controlled movement of the valve bridge  200 . However, the control surface  203  is also dimensioned (i.e., has sufficiently small diameter) to provide for engagement of the control surface  203  with the e-foot  204  when the valve bridge moves towards an uncontrolled position relative to the e-foot. That is, during movement, such as horizontal or vertical translation, pitch, roll or yaw of the valve bridge towards an uncontrolled state or position relative to the e-foot, the collar  202  may surround and operate to contact the e-foot  204  (regardless of the collapsed/un-collapsed or locked/unlocked state of the collapsing mechanism), thereby limiting any translation or other movement of the valve bridge  200  and maintaining the valve bridge  200  in a controlled state. This is illustrated in  FIG.  7    where movement of the valve bridge towards an uncontrolled position or state has brought the valve bridge out of contact with the engine valve stems  602 , for example. However, as shown in both  FIGS.  6  and  7   , the collar  202  is configured to have sufficient vertical extent to contact the e-foot  204  when the valve bridge would otherwise move to an uncontrolled state or position relative to the e-foot, and thereby reduce any tilting or misalignment of the valve bridge. 
     In accordance with other aspects of the disclosure, as shown in  FIGS.  6  and  7   , the valve bridge  200  may include an additional guide feature in the form of an extended portion  208  ( FIG.  2   ) having control surfaces  283  and configured to extend between but in close proximity to engine valve springs  302  and/or engine valve spring retainers  304 . Examples of various embodiments of such an extended portion are described in U.S. Pat. Nos. 10,883,392, 11,053,819 and 11,319,842, the disclosures and subject matter of which are incorporated by reference herein in their entirety. As described in these documents, the extended portion  208  is configured to remain out of contact with the valve springs  302  and/or retainers  304  during controlled operation of the valve bridge  200  but configured to contact the valve springs  302  and/or retainers  304  when the valve bridge moves towards an uncontrolled position, thereby limiting tilting/rotation or other undesired movement of the valve bridge  200  towards an uncontrolled state. The extended portion  208  may be provided with a tapered and/or conical deflection surface  281  ( FIGS.  2  and  3   ) at an end thereof. This feature prevents the bridge extended portion  208  from catching on corners or other sharp features in the overhead environment (i.e., in proximity to the space between valve springs where the extended portion  208  is typically located) when the bridge  200  undergoes a jump or movement towards an uncontrolled position. Deflection surface  281  thus prevents an uncontrolled position of the bridge  200  and guides the bridge  200  back to a controlled position in the event of a deviation from a controlled state or position. 
       FIGS.  8 A- 8 C  illustrate a sequence of a valve bridge jump for a valve bridge having the guiding features described. In  FIG.  8 A , the bridge  200  is in a controlled position relative to the valve stem tips  602 , with each valve stem tip  602  being aligned with and seated within a valve tip pocket  212 . Here, the bridge locking mechanism is locked in an extended position relative to the bridge  200 .  FIG.  8 B  shows the beginning of a bridge jump condition in which the bridge  200  becomes displaced from the valve stem tips  602 . This may occur when there is slippage in the locking mechanism resulting from partial engagement of the locking mechanism locking elements. As a result, and owing to the valve spring forces, the valve stem tips  602  may snap upward abruptly as the valves slam closed against their respective valve seat. Such action may jettison the valve bridge upward and cause the valve bridge to displace from the valve tips.  FIG.  8 C  shows the full extent of a possible bridge jump with the upper limit being reach as the locking mechanism collapses to its internal limit within the valve bridge central housing.  FIG.  9    is another cross-sectional view showing the position of an e-foot within the collar at a peak jump height. 
     As will be appreciated, while the illustrated bridge jump is a pure translation upward and involves the valve tip pockets  212  being equidistant from their respective valve stem tip  602 , it will be appreciated from the instant disclosure, that the constraint and guide features described herein may alleviate or accommodate (guide against) other undesirable bridge motion, such as pitch of the valve bridge  200  relative to the longitudinal axis in which case one of the valve tip pockets  212  would be further from its respective valve stem tip  602  than the other valve pocket  212 . Collar  202  and control surface  203  would thus restrict pitch of the valve bridge relative to the longitudinal axis since control surface  203  would encounter the e-foot before the bridge pitched to an uncontrolled position. Collar  202  and control surface  203  are also configured to prevent roll of the valve bridge  200  relative to its longitudinal axis. As will be recognized, such motion can also be viewed as pitch of the valve bridge  200  relative to its lateral axis. 
     According to aspects of the disclosure, valve bridges may also be provided with guiding features that accommodate movement toward an uncontrolled state or position (relative to the valve tips) and guide the valve bridge back towards a controlled state or position (relative to the valve tips). Referring again to  FIGS.  2 - 9  and  10 A- 10 D , the valve bridge  200  may include control surfaces in the form of lead-in chamfers  210  that substantially surround the valve tip pockets  212 . The lead-in chamfers  210  are each configured and adapted to receive a respective engine valve stem  602  and guide the valve stem  602  back into the valve pockets when misalignment or movement of the valve bridge towards an uncontrolled position relative to one or both of the valve stems  602  occurs.  FIGS.  10 A- 10 D  illustrate in cross-section a sequence in which a jumped valve bridge  200  is guided back to a controlled state. The lead-in chamfer  210  at each valve tip pocket  212  is large enough to interface with an outer diameter of the tip of valve stem  602  when movement of the valve bridge  200  is at a worst-case deviation from the controlled position (i.e., one or more or a combination of the translation, pitch, roll and yaw). The lead in chamfers  210  are configured to guide the valve bridge  200  back onto one or both of the valve tips following a bridge jump, misalignment, or other event in which the valve bridge would tend to move towards an uncontrolled position. Starting at  FIG.  10 A , the valve bridge  200  is moving towards an uncontrolled state as a result of the valve tip pocket  212  coming out of contact with the valve stem tip  602 . Moreover, the valve tip pocket  212  may also become misaligned with the valve stem tip  602  due to bridge translation, or yaw (about the vertical axis) as also shown in  FIG.  10 A . As will be recognized, the valve bridge  200  may also undergo roll or pitch. In accordance with aspects of the disclosure, as also shown in  FIG.  10 A , the bridge  200  is constrained against excessive translation (i.e., along the lateral and longitudinal axes) as well as excessive roll (about the longitudinal axis) by the collar  202  contacting the e-foot  204 , thereby limiting the errant, uncontrolled motion of the valve bridge  200 . This constraint, in turn, also limits misalignment of the valve tip pocket  212  relative to the valve stem tip  602 . In  FIG.  10 B , the valve bridge  200  may move into a position in which it contacts the valve stem tip  602  (where, for example, rotation of the rocker arm  206  and/or stroke or locking of the locking mechanism) forces the valve bridge  200  toward the engine valves). In this example, the lead-in chamfer  210  contacts an outer edge of the valve stem tip  602 . As shown in  FIGS.  10 C and  10 D , the sloped configuration of the lead-in chamfer  210 , combined with the continued contact between the outer diameter of the valve stem tip  602 , urges the valve bridge  200  to rotate/translate or otherwise return to a position in which the valve tip pocket  212  is in alignment with valve stem tip  602 . 
       FIG.  11    is a schematic showing geometrical representations of a bottom view of an example lead-in chamfer  210  configuration superimposed on representations of the valve spring outer circumference  620  and a cross-section of an example valve bridge extended portion  208  with control surfaces  283 . In accordance with aspects of the disclosure, the dimensions of the valve bridge lead-in chamfer, such as the diameter of a lead-in chamfer edge circle  211  may be configured to accommodate a determined maximum movement of the valve bridge relative to the valve stem tips. In accordance with aspects of the disclosure, this determined maximum movement may be defined by the constraints provided by the control surface  203  on collar  202  and/or the control surfaces on extended portion  208 . In this example, a maximum yaw (about the vertical axis extending into the page) of the extended portion  208  is determined based on the point of engagement of the extended portion  208  with the valve spring  620  outer circumference, or in an alternative constraint configuration, with the valve spring retainer ( 304  in  FIG.  6   ) when the valve spring retainer is made with an outer circumference that is larger than the spring outer circumference The extent (in this case a diameter) of the lead-in chamfer  210  may be selected to accommodate this maximum movement and may also include an allowance for additional clearance  213 . Thus, in accordance with aspects of the disclosure, the maximum (worst-case) movement (translation, pitch, roll, yaw relative to the longitudinal, lateral and vertical axes) of the valve bridge  200  relative to the valve stem tips  602  may be defined based on the above-described constraints, namely, the collar control surface and the extended portion control surface(s). Then, the lead-in chamfer(s) may be configured to accommodate the determined maximum movement, with some allowance for variation. Stated another way, the lead-in chamfer is configured to be large enough to catch and guide the valve stem tip at all possible positions of the bridge relative to the valve stem tip as defined by the constraint features on the valve bridge, namely, the extended portion control surface(s)  283  and/or the collar control surface  203 . In this manner, valve bridges can be readily configured to prevent bridge jump and uncontrolled operation. 
     While the embodiment of the valve bridge  200  shown in  FIGS.  2 - 6    and described herein illustrates the combination of the collar  202 , extended portion  208  and lead-in chamfers  210 , it is understood that all three of these features do not need to be included in all implementations of valve bridges in accordance with the instant disclosure. That is, rather than combining all three of these features, the collar  202  could be implemented as a single feature or in combination with either the extended portion  208  or the lead-in chamfers  210 . Furthermore, though these three features have been illustrated in the context of a valve bridge comprising a collapsing mechanism, it is noted that this is not a requirement. That is, it is understood that these features (once again, individually, collectively or in sub-combinations thereof) may be equally employed in valve bridges that do not incorporate a collapsing mechanism. 
       FIG.  12    illustrates another constraining configuration in accordance with aspects of the disclosure. In this example, a bridge brake pin  280  may be used in conjunction with collar  203  to provide an additional constraint on bridge movement. Bridge brake pin  280  may have a first diameter portion  282  extending through a bore  270  and arranged to engage a braking piston assembly  400 . A brake pin base  284  may have a larger diameter than the first diameter portion  282  and may be disposed within a counterbore  290  in the bridge. The dimensions of the brake pin base  284  and the first diameter portion  282 , as well as the dimensions of bore  270  and counterbore  290  can be configured to provide a determined constraint on movement of the valve bridge  200  during a braking operation or during other events. As will be recognized, the brake pin feature may provide a constraint on translation and yaw (about the vertical axis) which augments the constraint on motion provided by the collar  203 , thereby providing improved control of valve bridge motion and preventing bridge jump and uncontrolled movement during engine operation. 
       FIG.  13    illustrates a process  1300  for configuring bridge constraints and guides in accordance with the instant disclosure. At  1302 , the position of the locked bridge (relative to the valve stem tips) at cam base circle is evaluated. At  1304 , the position of the locked bridge at peak cam lift is evaluated. At  1306 , the position of the fully collapsed bridge is evaluated. At  1308 , the e-foot collar control surface(s) is(are) configured to constrain the bridge movement to a controlled state. At  1310 , the extended portion control surfaces are configured. At  1312 , the valve tip lead-in control surfaces (guides) are configured based on worst-case bridge movement as determined based on the evaluations at steps  1302  to  1310 . At  1314 , non-interference of the bridge control surfaces with other components in the overhead environment during normal engine operation may be verified. 
     Although the present implementations have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.