Patent Publication Number: US-11391186-B2

Title: Valve train assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/209,222 filed Dec. 4, 2018, which is a continuation of International Patent Application No. PCT/EP2017/065667 filed on Jun. 26, 2017, which claims the benefit of U.S. Patent Application No. 62/354,707 filed on Jun. 25, 2016, U.S. Patent Application No. 62/355,677 filed on Jun. 28, 2016, and U.S. Patent Application No. 62/405,397 filed Oct. 7, 2016. This application claims the benefit of U.S. Patent Application No. 62/594,147 filed Dec. 4, 2017 and U.S. Patent Application No. 62/636,308 filed Feb. 28, 2018. The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The disclosure relates to a valve train assembly comprising: at least a number of exhaust valves each having a valve stem; at least one camshaft with at least a pair of a primary lift cam and an engine brake lift cam; a number of rocker arms, each rocker arm having a valve stem actuation portion, a pivot axis parallel to the main cam shaft and a cam follower for following one of the primary lift cam and the engine brake lift cam; wherein each rocker arm having a cam follower following an engine brake lift cam is provided with an engine brake capsule, which is selectively translatable between a retracted and extended position, the retracted position disabling actuation of the valve by the engine brake lift cam and the corresponding rocker arm and the extended position enabling actuation of the valve. 
     BACKGROUND 
     Such a valve train assembly is known and used to provide engine brake functionality to a combustion engine. In the field, this type of engine brake is also called a Jake brake. For being able to brake with the engine, the compressed air at the end of the compression stroke of the cylinder needs to be released to the exhaust, such that the engine basically functions as an air compressor and thus consumes energy, which is derived from the drive train of the vehicle causing the vehicle to brake. 
     With the engine brake capsule one can select whether the engine brake lift cam can actuate an exhaust valve or not. In case the engine brake capsule is in extended position, the cam follower following the engine brake lift cam can actuate via the corresponding rocker arm an exhaust valve at the right moment to release the compressed air to the exhaust of the engine. 
     In retracted position of the engine brake capsule there will be too much lash between the engine brake lift cam and the corresponding exhaust valve for the cam to actuate the exhaust valve. Although this disables the engine braking and allows for normal operation of the engine, it will leave a substantial play for the corresponding rocker arm, such that the rocker arm can freely tilt up and down causing noise and additional wear. 
     It is therefore an object of the disclosure to reduce the above mentioned disadvantages. This object is achieved according to the disclosure with a valve train assembly according to the preamble, which is characterized by a number of biasing assemblies each one cooperating with one of the rocker arms of which the cam follower follows an engine brake lift cam to accommodate mechanical lash. 
     With the biasing assemblies the rocker arms with the cam follower following the engine brake lift cam is biased to a default position to accommodate the mechanical lash. This ensures that the rocker arm cannot tilt freely, reducing the noise and reducing the wear on the rocker arm. 
     SUMMARY 
     in an example of the valve train assembly according to the present disclosure each rocker arm has a single valve stem actuation portion and two cam followers, one of which cam followers following a primary lift cam and one of which cam followers following an engine brake lift cam. Such a rocker arm has for example a Y-shape and allows for a single exhaust valve to be used as both the primary exhaust valve during normal operation of the engine as well as the release valve in the engine brake mode to release compressed air from the cylinder. 
     In another example of the valve train assembly according to the disclosure a pair of a primary lift cam and an engine brake lift cam has two corresponding rocker arms for actuating two corresponding valves. In this example the primary lift cam has a dedicated, corresponding rocker arm, which actuates a dedicated, corresponding exhaust valve, and has the engine brake lift cam a corresponding rocker arm to actuate a corresponding, separate exhaust valve. 
     In a preferred example of the valve train assembly according to the disclosure the valve stem actuation portion of the rocker arm corresponding to the primary lift cam overlaps with the valve stem actuation portion of the rocker arm corresponding to the engine brake lift cam, such that on actuation by the primary lift cam both valves are actuated. With this example, the primary lift cam can also actuate the exhaust valve corresponding to the engine brake lift cam due to the overlapping valve stem actuation portion. This allows for two exhaust valves to be used during normal engine operation, while still an engine brake functionality is provided. 
     In a further preferred example of the valve train assembly according to the disclosure each biasing assembly comprises a lever pivotably mounted to the rocker arm, a lost motion spring biased between the lever and the rocker arm and limiting means for limiting the rotation of the lever relative to the pivot axis of the rocker arm. 
     The limiting means provide for a small lash to be set by setting the spacing between the lever and the limiting means. During actuation of the rocker arm and the engine brake exhaust valve, the limiting means will contact the lever, blocking further movement of the lever, such that the lost motion spring is compressed and ensures that after actuation of the engine brake exhaust valve, the mechanical lash is accommodated for. 
     In a further example of the valve train assembly according to the disclosure the biasing assemblies further comprise a lash adjustment screw arranged between an end of the lever and the rocker arm. The adjustment screw allows for setting the mechanical lash between the lever and the limiting means, such that the operation of the valve train assembly can be optimized. 
     In yet another example of the valve train assembly according to the disclosure the lever and lost motion spring are embodied as a leaf spring or as a spiral spring arranged around the pivot axis of the rocker arm. By embodying the lever and lost motion spring as a single element, i.e. a leaf spring or spiral spring, the number of parts is reduced in the valve train assembly. 
     In still a further example of the valve train assembly according to the disclosure the biasing means comprises a return cam follower arranged on the opposite side of the cam shaft and facing the cam follower following the engine brake lift cam. With both a cam follower for the engine brake lift cam and a return cam follower, the corresponding rocker arm is controlled in both tilting directions. This ensures that the rocker arm cannot tilt freely and mechanical lash is accommodate for. 
     A compliance spring can be arranged between the return cam follower and rocker arm. This allows for both cam followers to be positioned on a desired opposite position, while any lash is eliminated. If no compliance spring is used, some lash could occur do to asymmetry between contact positions of both cam followers on the same cam lobe. 
     In a further preferred example of the valve train assembly according to the disclosure a return lift cam is provided on the cam shaft and the return cam follower follows the return lift cam. The separate return lift cam allows for a small lash by designing the engine brake lift cam lobe profile and the return lift cam lobe profile, while still the tilting movement in both directions of the rocker arm is fully controlled. 
     In yet another example of the valve train assembly according to the disclosure the biasing means comprise a torsion spring arranged between the pivot axis of the rocker arm and the rocker arm. Preferably, the torsion spring comprises at least one coil spring tangentially arranged between the pivot axis and the rocker arm. 
     A further example of the valve train assembly according to the disclosure further comprises a friction element arranged between the rocker arm and said pivot axis. The friction element prevents any free tilting movement of the rocker arm, even when a small lash is provided for. This will further reduce noise and wear. However, if the cam actuates the rocker arm, the friction element will allow for movement of the rocker arm. Preferably, the pivot axis is provided by a rocker shaft, wherein the friction element is provided by a tangential groove arranged in the rocker shaft and a spring loaded ball arranged between the rocker arm and the tangential groove. 
     The spring loaded ball will press into the tangential groove, such that free movement of the rocker arm is counteracted. However, if the cam actuates the rocker arm, the spring loaded ball can move through the tangential groove allowing for the tilting movement of the rocker arm. 
     In another preferred example of the valve train assembly according to the disclosure the friction element is a centripetal clutch. The clutch will prevent free movement of the rocker arm, but on sudden rotation due to actuation of the cam, the clutch will disengage and allow for the rocker arm to follow the cam. 
     In still a further example of the valve train assembly according to the disclosure the engine brake capsule comprises a cylinder and a piston arranged in the cylinder, wherein the piston is arranged to either the cam follower or the valve stem actuation portion and wherein a fluid channel is provided in the rocker arm to supply the cylinder space of the engine brake capsule with pressurized fluid in order selectively translate the piston between a retracted and extended position. 
     The pressurized fluid can for example be fed via a channel extending through the rocker arm shaft, such that all engine brake capsules in the valve train assembly can be extended or retracted at the same time. 
     A rocker arm assembly operable in a first mode and a second mode selectively opens first and second engine valves based on rotation of a cam shaft having a first cam lobe and a second cam lobe. The rocker arm assembly includes a rocker shaft, a first and second rocker arm assemblies and a biasing assembly. The first rocker arm assembly has a first rocker arm that receives the rocker shaft and is configured to rotate around the rocker shaft in the first mode based on engagement with the first cam lobe. The second rocker arm assembly has a second rocker arm that receives the rocker shaft and is configured to rotate around the rocker shaft and selectively act on one of the first and second engine valves in the second mode based on selective engagement with the second cam lobe. The biasing assembly cooperates with the second rocker arm to bias the second rocker arm to a neutral position. In the neutral position, the second rocker arm is spaced from contact relative to both of the second cam lobe and the second engine valve. 
     According to other features, the biasing assembly further includes a spring plate assembly having a first spring plate, a second spring plate and at least one biasing member. The first spring plate is fixed relative to the rocker shaft. The second spring plate is fixed for rotation with the second rocker arm. The at least one biasing member is disposed relative to the first and second spring plates and is configured to load and unload based on rotation of the second rocker arm around the rocker shaft. The spring plate assembly can define at least one window that is configured to receive the at least one biasing member. The at least one window is defined in part by a first bearing surface on the first spring plate and a second bearing surface on the second spring plate. The at least one biasing member bears against the respective first and second baring surfaces during rotation of the second rocker arm around the rocker shaft. 
     In other features, the spring plate assembly comprises at least one spring retainer configured to retain the at least one biasing member within the at least one window. The first plate can define at least one slot. The second plate can define at least one aperture. A fastener extends through the at least one slot and the at least one aperture and is threadably secured into a threaded bore defined in the second rocker arm. The second spring plate rotates relative to the first spring plate while the fastener travels along the at least one slot during rotation of the second rocker arm during operation in the second mode. 
     According to additional features, the second rocker arm includes a capsule configured to move between a retracted position and an extended position. In the retracted position, the biasing assembly biases the second rocker arm to the neutral position. In the extended position, the second rocker arm is caused to rotate toward the second cam lobe preloading the biasing assembly. 
     In additional features, an orientation system can include a key extending from the camshaft. A keyway can be define don the first plate. A pair of opposed stops can define a rotational limitation slot on the second plate. The key is fixed to the first plate at the keyway. Rotation of the second rocker arm is limited by engagement of the key with the opposed stops on the second plate. 
     In one arrangement, the first rocker arm assembly is an exhaust valve rocker arm assembly and the second rocker arm assembly is an engine brake rocker arm assembly. The exhaust valve rocker arm assembly includes an exhaust rocker arm and a valve bridge. The valve bridge has a lever pivotally coupled thereto such that during operation in the second mode, the engine brake rocker arm does not transfer motion to the valve bridge. In one configuration, the first and second engine valves are exhaust valves and one of the first and second modes includes early exhaust valve opening (EEVO). In another configuration, the first and second engine valves are intake valves and wherein one of the first and second modes includes late intake valve closing (LIVC). 
     A rocker arm assembly operable in a first mode and a second mode selectively opens first and second engine valves based on rotation of a cam shaft having a first cam lobe and a second cam lobe. The rocker arm assembly includes a rocker shaft, a first and second rocker arm, a capsule and a spring plate assembly. The first rocker arm is configured to rotate around the rocker shaft in the first mode based on engagement with the first cam lobe. The second rocker arm is configured to rotate around the rocker shaft and selectively act on one of the first and second engine valves in the second mode based on selective engagement with the second cam lobe. The capsule is arranged on the second engine brake rocker arm and is configured to move between an extended position and a retracted position. The spring plate assembly cooperates with the second rocker arm to bias the second rocker arm to a neutral position when the capsule is in the retracted position. In the neutral position, the second rocker arm is spaced from contact relative to both of the second cam lobe and the second engine valve. The spring plate assembly includes a first spring plate, a second spring plate and at least one biasing member. The first spring plate is fixed relative to the rocker shaft. The second spring plate is fixed for rotation with the second rocker arm. The at least one biasing member selectively biases against the first and second spring plates upon rotation of the second rocker arm. 
     The spring plate assembly can define at least one window that is configured to receive the at least one biasing member. The at least one window is defined in part by a first bearing surface on the first spring plate and a second bearing surface on the second spring plate. The at least one biasing member bears against the respective first and second baring surfaces during rotation of the second rocker arm around the rocker shaft. 
     In other features, the spring plate assembly comprises at least one spring retainer configured to retain the at least one biasing member within the at least one window. The first plate can define at least one slot. The second plate can define at least one aperture. A fastener extends through the at least one slot and the at least one aperture and is threadably secured into a threaded bore defined in the second rocker arm. The second spring plate rotates relative to the first spring plate while the fastener travels along the at least one slot during rotation of the second rocker arm during operation in the second mode. 
     In additional features, in the extended position, the second rocker arm is caused to rotate toward the second cam lobe preloading the biasing assembly. An orientation system can include a key extending from the camshaft. A keyway can be define don the first plate. A pair of opposed stops can define a rotational limitation slot on the second plate. The key is fixed to the first plate at the keyway. Rotation of the second rocker arm is limited by engagement of the key with the opposed stops on the second plate. 
     Further areas of applicability of the teachings of the present disclosure will become apparent from the detailed description, claims and the drawings provided hereinafter, wherein like reference numerals refer to like features throughout the several views of the drawings. It should be understood that the detailed description, including disclosed examples and drawings referenced therein, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the present disclosure, its application or uses. Thus, variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a first example of a valve train assembly according to the disclosure; 
         FIG. 2  shows a perspective view of the back side of the assembly of  FIG. 1 ; 
         FIG. 3  shows a perspective view of engine brake rocker arms of  FIG. 1  arranged side by side; 
         FIGS. 4-6  show schematically the operation of a second example of the valve train assembly according to the disclosure; 
         FIG. 7  shows a third example of an engine brake rocker arm for a valve train assembly according to the disclosure; 
         FIG. 8  shows a fourth example of an engine brake rocker arm for a valve train assembly according to the disclosure; 
         FIG. 9  shows a fifth example of an engine brake rocker arm for a valve train assembly according to the disclosure; 
         FIG. 10  shows a sixth example of an engine brake rocker arm for a valve train assembly according to the disclosure; 
         FIG. 11  shows a seventh example of an engine brake rocker arm for a valve train assembly according to the disclosure; 
         FIG. 12  shows a eighth example of an engine brake rocker arm for a valve train assembly according to the disclosure; 
         FIG. 13  is a first perspective view of a partial valve train assembly incorporating a rocker arm assembly including an intake rocker arm, an exhaust rocker arm and an engine brake rocker arm having a biasing assembly constructed in accordance to one example of the present disclosure; 
         FIG. 14  is a second perspective view of the partial valve train assembly of  FIG. 13  and shown with the intake rocker arm and associated intake valves removed for illustrative purposes; 
         FIG. 15  is a first perspective view of the engine brake rocker arm and associated biasing assembly; 
         FIG. 16  is a second perspective view of the engine brake rocker arm and associated biasing assembly of  FIG. 15 ; 
         FIG. 17  is an exploded perspective view of the engine brake rocker arm and associated biasing assembly of  FIG. 16 ; 
         FIG. 18  is a front view of the engine brake rocker arm and biasing assembly of  FIG. 15  and shown in a neutral position; 
         FIG. 19  is a front view of the engine brake rocker arm and biasing assembly of  FIG. 15  and shown during an engine braking event wherein biasing members of the biasing assembly are loaded as the rocker arm rotates toward engagement with the engine brake cam lobe; and 
         FIG. 20  is a front view of the engine brake rocker arm and biasing assembly of  FIG. 19  and shown as the valve goes through a valve lift event and the biasing members become unloaded as the rocker arm rotates clockwise from the position shown in  FIG. 19  to the position shown in  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is set forth in the context of rocker arms for opening exhaust valves configured in a compression engine braking system. The discussion focuses on a camshaft having a primary lift cam and an engine brake lift cam. It will be appreciated that the disclosure is not so limited. For example, the present disclosure can also be additionally or alternatively applicable to exhaust valves in other non-compression brake systems. Moreover, the disclosure may also be applicable to intake valves. In this regard, the camshaft can be configured with a primary lift cam and a secondary lift cam. For example, the present disclosure can also be applicable to valvetrains configured for early exhaust valve opening (EEVO), late intake valve closing (LIVC) or other variable valve actuation (VVA) configurations. 
     Heavy duty (HD) diesel engines with single overhead cam (SOHC) valve train requires high braking power, in particular at low engine speed. The present disclosure provides an added motion type de-compression engine brake. To provide high braking power without applying high load on the rest of the valve train (particularly the camshaft), the present disclosure provides a dedicated rocker arm for engine brake that acts on one exhaust valve. In this regard, half of the input load is experienced compared to other configurations that have two exhaust valves opening. 
       FIG. 1  shows a perspective view of a first example of a valve train assembly  1  according to the disclosure. The valve train assembly  1  has a primary exhaust valve  2  and a brake exhaust valve  3 . A cam shaft  4  is provided with pairs of a primary lift cam  5  and an engine brake lift cam  6 . 
     A rocker shaft  7  is provided parallel to the cam shaft  4 . A main rocker arm  8  and an engine brake rocker arm  9  are pivotably arranged on said rocker shaft  7 . The engine brake rocker arm  9  acts directly on the brake exhaust valve  3 , while the main rocker arm  8  acts on a bridge  10 , such that both the primary exhaust valve  2  and the engine brake valve  3  can be actuated simultaneous. To this end, the engine brake rocker arm  9  extends through the bridge part  10  to be able to actuate the brake exhaust valve  3  separately. 
       FIG. 2  shows a perspective view of the back side of the assembly  1  of  FIG. 1 . The main rocker arm  8  has a roper  11 , which follows the profile of the primary lift cam  5  to actuate the primary exhaust valve  2 . The engine brake rocker arm  9  also has a roller  12  which follows the profile of the engine brake rocker arm  9  to actuate the engine brake exhaust valve  3 . The rocker arm  9  is provided with a lever  13  pivotably arranged on top of the rocker arm  9 . A lost motion spring  14  is arranged between the lever  13  and the rocker arm  9  to accommodate for any lash. The pivoting of the lever  13  is limited by the bridge part  15 , which ensures that the lost motion spring  14  is compressed on actuation of the rocker arm  9  and that the rocker arm  9  returns to its default position. 
       FIG. 3  shows a perspective view of engine brake rocker arms  9  of  FIG. 1  arranged side by side. One end of each engine brake rocker arm  9  is provided with an engine brake capsule  16  which will be explained in  FIGS. 4-6 .  FIG. 4  shows a second example  20  of a valve train assembly according to the disclosure. The example  20  has an engine brake rocker arm  21  pivotably arranged on a rocker shaft  22 . One end of the rocker arm  21  is provided with a roller  23  for following an engine brake lift cam  24 . The other end of the rocker arm  21  is provided with an engine brake capsule  16 . 
     The engine brake capsule  16  has a cylinder  25  in which a piston  26  is movably arranged. Via a supply channel  27  in the rocker shaft  22  and a supply channel  28  in the rocker arm  21 , the cylinder space  25  can be supplied with pressurized fluid, which causes the piston  26  to extend or to retract. The piston  26  is provided with a valve stem actuation portion  29 , which actuates the valve stem head of the engine brake valve  3 . 
     The rocker arm  21  is furthermore provided with a biasing assembly in the form of a spiral spring  30 , which is folded around the rocker shaft  22 . On end  31  of the spiral spring  30  is connected to the rocker arm  21 , while the other end  32  is limited by a rod  33 , similar to the bridge portion  15  of the example  1 . 
       FIGS. 5 and 6  both show the example  20  when the lobe  34  on the engine brake lift cam  24  pushes the roper  23  upwards and causes the rocker arm  21  to tilt. The tilting can be seen by the end  32  of the spiral spring  30 , which is free from the hook part  35 . In  FIG. 5 , the cylinder space  25  is not provided with pressurized fluid, such that the piston  26  is in the retracted position and the valve  3  is not actuated and remains seated to its seat  36 . Now when the lobe  34  passes the roller  23 , the spiral spring  30  will move the rocker arm  21  back into the position shown in  FIG. 4 . 
     In  FIG. 6 , the cylinder chamber  25  is provided with pressurized fluid, such that the piston  26  is in the extended position and actuates the valve  3  such that the valve head is moved away from the valve seat  36  and pressurized air from the engine cylinder can pass to an exhaust.  FIG. 7  shows the engine brake rocker arm  9  in detail. The rocker arm  9  is provided with an engine brake capsule  16 , which has a cylinder space  25  and a piston  26 . The cylinder space  25  is connected to a fluid channel  17 . 
     The lever  13  is arranged to the rocker arm  9  via pivot axle  19 . A lash adjustment screw  18  is provided between the lever  13  and the rocker arm  9  to set some lash between the lever  13  and the bridge  15 . 
       FIG. 8  shows a fourth example  40  of an engine brake rocker arm for a valve train assembly according to the disclosure. The rocker arm body  41  is provided with an opening  42  for the rocker shaft, an engine brake capsule  16  on one end and a roller  43  on the other end. A biasing assembly in the form of a leaf spring  44  is mounted on top of the rocker arm body  41  to accommodate lash. The free end of the leaf spring  44  is limited by a rod  45   
       FIG. 9  shows a fifth example  50  of an engine brake rocker arm for a valve train assembly according to the disclosure. The rocker arm has a Y-shaped rocker arm body  51  with on one hand of the Y-shape a first roller  52  and on the other hand of the Y-shape a follower  53 . This follower  53  is spring loaded by a compliance spring  54 . 
     The engine brake lift cam  55  on the camshaft  56  is followed by the roller  52 , while the additional return lift cam  57  is followed by the follower  53 . This arrangement ensures that the mechanical lash is accommodated for and that the rocker arm  51  cannot move freely. 
       FIG. 10  shows a sixth example  60  of an engine brake rocker arm for a valve train assembly according to the disclosure. This example is variant of the example  50  and similar parts are provided with the same reference signs. 
     The rocker arm  60  has a first roller  52  which follows the profile of the engine brake lift cam  61 . A separate arm  62  is pivotably arranged to the rocker arm  60  and spring loaded by a compliance spring  63 . The separate arm  62  is provided with a follower  64 , such that lash is accommodated for. As the roller  52  and follower  64  follow the same profile the compliance spring  63  and pivot able arranged separate arm  62  accommodate for any distance differences between the roller  52  and the follower  64 . 
       FIG. 11  shows a seventh example  70  of an engine brake rocker arm for a valve train assembly according to the disclosure. The engine brake rocker arm  70  is arranged on a rocker shaft  71 . The rocker shaft  71  is provided with a tangential groove  72  in which a ball  73  is positioned. This ball is urged by a spring  74  arranged to the rocker arm  70 . This ensures that the rocker arm  70  is urged to a default position and thus any lash is accommodated for. 
       FIG. 12  shows an eighth example  80  of an engine brake rocker arm for a valve train assembly according to the disclosure. This rocker arm  80  is provided with a torsion spring comprising an outer housing ring  81  and an inner housing ring  82 , which is fixedly arranged to the rocker shaft  83 . The outer housing ring  81  and the inner ring  82  are provided with interlocking protrusions  84 ,  85  between which coil springs  86  are arranged. 
     Now when the rocker arm  80  is tilted, the outer housing ring  81  will be rotated relative to the inner housing ring  82 , such that the coil springs  86  are compressed. As soon as the rocker arm  80  is released, the coil springs  86  will urge the rocker arm  80  back to its default position and accommodate for any lash. 
     With reference now to  FIG. 13 , a partial valve train assembly constructed in accordance to another example of the present disclosure is shown and generally identified at reference  210 . The partial valve train assembly  210  utilizes engine braking and is shown configured for use in a three-cylinder bank portion of a six-cylinder engine. It will be appreciated however that the present teachings are not so limited. In this regard, the present disclosure may be used in any valve train assembly that utilizes engine braking or other valvetrains such as those discussed above. The partial valve train assembly  210  is supported in a valve train carrier  212  and can include three rocker arms per cylinder. 
     Specifically, each cylinder includes an intake valve rocker arm assembly  220 , a first or exhaust valve rocker arm assembly  222  and a second or engine brake rocker arm assembly  224 . The exhaust valve rocker arm assembly  222  and the engine brake rocker arm assembly  224  cooperate to control opening of the exhaust valves and are collectively referred to as a dual exhaust valve rocker arm assembly  226 . The intake valve rocker arm assembly  220  is configured to control motion of intake valves  228 ,  230 . The exhaust valve rocker arm assembly  222  is configured to control exhaust valve motion in a drive mode. The engine brake rocker arm assembly  224  is configured to act on one of the two exhaust arms in an engine brake mode as will be described herein. A rocker shaft  234  is received by the valve train carrier  212  and supports rotation of the exhaust valve rocker arm assembly  222  and the engine brake rocker arm assembly  224 . 
     With continued reference to  FIG. 13  and additional reference to  FIG. 14 , the exhaust valve rocker arm assembly  222  can generally include an exhaust rocker arm  240 , a valve bridge  242 , and a spigot assembly  244 . A lever  248  can be pivotably coupled to the valve bridge  242  such that during a braking event an engine brake rocker arm  260  does not transfer motion to the valve bridge  242 . The engine brake rocker arm assembly  224  can include the engine brake rocker arm  260  having an engaging portion  262  ( FIG. 15 ). The valve bridge  242  engages a first and second exhaust valve  250  and  252  ( FIG. 13 ) associated with a cylinder of an engine (not shown). 
     A camshaft  270  includes an exhaust main lift cam lobe  272  and an engine brake cam lobe  274 . The exhaust rocker arm  240  has a first roller  276 . The engine brake rocker arm  260  has a second roller  278 . The first roller  276  rotatably engages the exhaust main lift cam lobe  272 . As will be described in greater detail herein, the second roller  278  is configured to selectively rotatably engage the engine brake cam lobe  274 . The exhaust rocker arm  240  rotates around the rocker shaft  234  based on a lift profile of the exhaust main lift cam lobe  272 . The engine brake rocker arm  260  rotates around a rocker shaft  34  based on a lift profile of the engine brake cam lobe  274 . 
     With additional reference now to  FIGS. 15-17 , the engine brake rocker arm  260  includes an engine brake capsule  246 . In general, the engine brake capsule  246  has a plunger  280  that is movably disposed in a cylinder  282 . In the example shown, the plunger  280  can include the engaging portion  262 . The rocker shaft  234  defines an oil supply channel  284  ( FIG. 13 ). An oil supply passage  286  is defined in the engine brake rocker arm  260 . The cylinder  282  can be supplied with pressurized fluid causing the plunger  280  to extend or to retract. 
     The engine brake rocker arm assembly  224  includes a biasing assembly  300  that cooperates with the engine brake rocker arm  260  to bias the engine brake rocker arm  260  to accommodate mechanical lash. As discussed herein, the biasing assembly  300  biases the engine brake rocker arm  260  to a neutral position out of contact with either the engine brake cam  274  or the valve  252 . Moreover, the biasing assembly  300  can be attached to the engine brake rocker arm  260  and installed as a single assembly. 
     In the example embodiment, the biasing assembly  300  is a spring plate lost motion system that generally includes a spring plate assembly  302  collectively defined in part by first and second spring plates  303 A,  303 B. The spring plate assembly  302  defines a plurality of windows  304  collectively defined by respective first and second windows  305 A,  305 B. Each window  304  is configured to receive a biasing member  306  (e.g., a spring). Each or the first windows  305 A are partially defined by a first spring bearing surface  307 A. Each of the second windows  305 B are partially defined by a second spring bearing surface  307 B. A plurality of spring retainers  308  ( FIG. 18 ), collectively defined by first fingers  309 A ( FIG. 17 ) formed on the first plate  303 A and second fingers  309 B formed on the second plate  303 B are configured to retain the biasing members  306  within the windows  304 . 
     The first plate  303 A defines slots  310 . The second plate  303 B defines apertures  312 . Fasteners  314  are configured to pass through respective grommets  316 , slots  310 , and apertures  312  and threadably secure into respective threaded bores  320  defined in the engine brake rocker arm  260 . The second plate  303 B is fixed for rotation with the engine brake rocker arm  260 . The first plate  303 A is fixed to the rocker shaft  234 . As will be described herein, when the engine brake rocker arm  260  is caused to rotate around the rocker shaft  234 , the biasing members  306  selectively compress and retract. 
     With reference to  FIGS. 18-20 , an orientation system  420  cooperates with the biasing assembly  300  to hold the engine brake rocker arm  260  neutral in a desired rotational orientation. In the example embodiment, the orientation system  420  includes a key  422 , a keyway  424  ( FIG. 17 ) defined on the first plate  303 A, and a rotational limitation slot  426  defined on the second plate  303 B. As will become appreciated, the orientation system  420  fixes the engine brake rocker arm  360  to the first spring plate  303 A. 
     The key  422  can be coupled to the rocker shaft  234  by inserting a portion of the key  422  into a slot or opening  428  formed in the rocker shaft  234 . In some examples, the key  422  is press fit into slot  428  or has a tight clearance fit with the slot  428 . In the example illustration, key  422  is a generally semi-circular disc. At least a portion of the key  422  extends outwardly from the outer surface of the rocker shaft  234  when inserted therein. Engine brake rocker arm  260  is configured to receive the rocker shaft  234  such that key  422  is at least partially disposed within the keyway  424  and the rotational limitation slot  426 . The key  422  can be configured differently. For example, the key  422  can take other geometrical forms such as, but not limited to, a post that can be press-fit into a complementary bore defined in the rocker shaft  234 . Other mechanical features can be incorporated as part of or as a supplemental attachment to the rocker shaft  234  to couple the first spring plate  303 A in a fixed orientation relative to the rocker shaft  234 . The key  422  fixes the first plate  303 A relative to the rocker shaft  234 . 
     The rotation limitation slot  426  is defined by a pair of opposed stops  430  which are each configured to engage the key  422  to limit the rotational travel of the engine brake rocker arm  260 . The rotational limitation slot  426  is defined to provide full design rotation of the rocker arm  260  without the rocker arm  260  contacting the key  422 . As such, during operation, the rocker arm shaft  234  and key  422  remain stationary while the engine brake rocker arm  260  selectively rotates about the rocker arm shaft  234 . The stops  430 , are positioned to engage key  422  and thus limit rotation of rocker arm  260  and facilitate maintaining the rocker arm  260  in a neutral position. 
     As mentioned above, the first spring plate  303 A remains fixed relative to the rocker shaft  234 . When the brake capsule  246  is “off” or collapsed, the engine brake rocker arm  260  returns to the neutral position such that the roller  278  is held off the engine brake cam lobe  274 . See  FIG. 18 . Concurrently, the plunger  280  of the brake capsule  246  is held off of the lever  248 . In this regard, when the brake capsule  246  is “off” and engine braking is not performed, the engine brake rocker arm  260  is encouraged to return this neutral position by the biasing assembly  300  whereby the roller  278  does not engage the engine brake cam lobe  274  on one side and the plunger  280  of the brake capsule  246  does not engage the lever  248  on an opposite side. 
     The neutral position as described herein is used to denote a first non-contact space  450  ( FIG. 18 ) between the engine brake rocker arm  260  and the engine brake cam lobe  274  and a second non-contact space  452  between the engine brake rocker arm  260  and the valve  252 . It is appreciated that the first non-contact space  450  is shown in  FIG. 18  specifically between the roller  278  and the engine brake cam lobe  274 . However, the first non-contact space  450  can be defined between any adjacent components intermediate the engine brake rocker arm  260  and the engine brake cam lobe  274 . Similarly, while the second non-contact space  452  is shown in  FIG. 18  specifically between the lever  248  and the plunger  280 , the second non-contact space  252  can be defined between any adjacent components intermediate the engine brake rocker arm  260  and the valve  252 . 
     During operation, the biasing members  306  hold the engine brake rocker arm  260  in a position relative to the spring plate assembly  302 . When the engine brake capsule  246  extends, such as during an engine braking event ( FIG. 19 ), the engine brake rocker arm  260  is caused to rotate in a direction toward the cam (counterclockwise as viewed from  FIG. 18  to  FIG. 19 ). The fasteners  314  and grommets  316  travel along the respective slots  310  of the first spring plate  303 A. Concurrently, the second spring plate  303 B is fixed for rotation with the engine brake rocker arm  260 . The biasing members  306  become pre-loaded bearing against respective first and second spring bearing surfaces  307 A,  307 B. As the valve  252  goes through a valve lift event, the biasing members  306  become unloaded as the engine brake rocker arm rotates (clockwise from  FIG. 19  to  FIG. 20 ). The configuration described herein with respect to the biasing assembly  300  is configured to operate opposite to other prior art configurations that rely on valve lift to cause pre-loading of a biasing mechanism. 
     It should be understood that the mixing and matching of features, elements, methodologies and/or functions between various examples may be expressly contemplated herein so that one skilled in the art would appreciate from the present teachings that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise above.