EP3146185B1

EP3146185B1 - Heavy duty valvetrain with de-compression engine brake feature

Info

Publication number: EP3146185B1
Application number: EP15723509.4A
Authority: EP
Inventors: Majo Cecur
Original assignee: Eaton Intelligent Power Ltd
Current assignee: Eaton Intelligent Power Ltd
Priority date: 2014-05-21
Filing date: 2015-05-19
Publication date: 2020-04-01
Anticipated expiration: 2035-05-19
Also published as: CN106536878B; JP6652556B2; CN106536878A; WO2015177127A1; EP3146185A1; JP2017519157A

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Patent Application No. 62/001276 filed on May 21, 2014 .

FIELD

The present disclosure relates generally to a rocker arm assembly for use in a valve train assembly and more particularly to a rocker arm assembly that incorporates a dedicated rocker arm that acts on a single exhaust valve to perform an engine brake function.
CN203097985U shows an engine braking device with special cam for braking single valve. WO2012078280A1 shows engine braking devices and methods. WO2012162616A1 shows a primary and auxiliary rocker arm assembly for engine valve actuation.
Compression engine brakes can be used as auxiliary brakes, in addition to wheel brakes, on relatively large vehicles, for example trucks, powered by heavy or medium duty diesel engines. A compression engine braking system is arranged, when activated, to provide an additional opening of an engine cylinder's exhaust valve when the piston in that cylinder is near a top-dead-center position of its compression stroke so that compressed air can be released through the exhaust valve. This causes the engine to function as a power consuming air compressor which slows the vehicle.
In a typical valve train assembly used with a compression engine brake, the exhaust valve is actuated by a rocker arm which engages the exhaust valve by means of a valve bridge. The rocker arm rocks in response to a cam on a rotating cam shaft and presses down on the valve bridge which itself presses down on the exhaust valve to open it. A hydraulic lash adjuster may also be provided in the valve train assembly to remove any lash or gap that develops between the components in the valve train assembly.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

SUMMARY

The invention is defined according to the claims.
A dual exhaust rocker arm assembly constructed in accordance to one example of the present disclosure is operable in a combustion engine mode and an engine braking mode. The dual exhaust valve rocker arm assembly selectively opens first and second exhaust valves and includes a rocker shaft, an exhaust valve rocker arm assembly, an engine brake rocker arm assembly and an engine brake capsule. The exhaust valve rocker arm assembly has an exhaust rocker arm that receives the rocker shaft and is configured to rotate around the rocker shaft. The exhaust rocker arm further defines a bore having an inner diameter. The engine brake rocker arm assembly has an engine brake rocker arm. The engine brake capsule is slidably received along the inner diameter of the bore of the exhaust valve rocker arm. The engine brake capsule is selectively translatable upon urging by the engine brake rocker arm. The engine brake capsule, in turn, urges one of the first and second exhaust valves open during engine braking mode.
According to additional features the dual exhaust valve rocker arm assembly further comprises an oil control valve that provides oil flow for actuation of the engine brake capsule from a pressurized oil supply. The engine brake capsule includes an engine brake capsule piston and an engine brake capsule body. A pressurized oil chamber is defined between the engine brake capsule piston and the engine brake capsule body. The engine brake rocker arm is configured to act on the engine brake capsule piston which acts on the engine brake capsule body which ultimately acts on one of the engine brake exhaust valves.
According to other features, the dual exhaust valve rocker arm assembly further comprises a valve tip positioned between one of the engine brake exhaust valves and the engine brake capsule body. A lock ball assembly can include a ball lock and a ball lock spring. The ball lock spring can urge the ball lock into a groove defined on the engine brake capsule body. A c-clip can be configured on the rocker arm assembly. The c-clip can limit a stroke of the engine brake capsule and provide a hard stop.
According to still additional features, the dual exhaust rocker arm assembly further includes an actuator assembly configured to move the engine brake capsule between an extended and a retracted position. The actuator assembly and the oil control valve are configured in the exhaust rocker arm separate from the engine brake capsule. The actuator assembly includes an actuator body, an actuator check ball, an actuator needle, an actuator return spring and an actuator locking nut. The actuator needle is configured to keep the actuator check ball in an open position and prevent oil pressure buildup in the engine brake capsule. The actuator check ball allows one-way replenishment at every cycle into the pressurized oil chamber. In engine braking mode, the oil control valve is energized open and oil pressure causes the actuator needle to move away from a corresponding seat such that the engine brake capsule is extended a predetermined length. De-energizing the oil control valve causes the actuator needle to allow oil out from the pressurized oil chamber and the engine brake capsule to move to the retracted position allowing combustion. In additional features, the dual exhaust rocker arm assembly includes a first adjustment screw provided on the engine brake rocker arm and a second adjustment screw provided on the exhaust rocker arm. Both of the first and second adjustment screws are adjustable to selectively provide lash settings for the dual exhaust rocker arm assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a top 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 constructed in accordance to one example of the present disclosure;
FIG. 2 is a side view of an exhaust rocker arm and an engine brake rocker arm of the valve train assembly of FIG. 1;
FIG. 3 is a schematic illustration of the exhaust rocker arm and the engine brake rocker arm of FIG. 2 according to one example;
FIG. 4 is a schematic illustration of the exhaust valve rocker arm assembly of FIG. 2 and shown with an engine brake capsule fully extended;
FIG. 5 is a schematic illustration of the exhaust valve rocker arm assembly of FIG. 2 and shown with the engine brake on max lift;
FIG. 6 is a detail cross-sectional view of a ball lock and ball spring that loads a ball against a groove defined in an outer diameter of a capsule body of the exhaust valve rocker arm assembly of FIG. 2 according to one example;
FIG. 7 is a side view of the ball engaging the groove on the outer diameter of the capsule body of FIG. 6;
FIG. 8 is a top perspective view of a first adjustment screw on the engine brake arm, a second adjustment screw of the exhaust arm and a third adjustment screw of the intake arm, all provided to provide valve lash set according to one example of the present disclosure; and
FIG. 9 is a cross-sectional view of the exhaust rocker arm assembly of FIG. 2 showing a stroke length of a fully collapsed and fully expanded engine brake capsule;
FIG. 10 is a side view of the exhaust valve rocker arm assembly shown with the exhaust rocker arm and the engine brake rocker arm on the base circle of the cam shaft;
FIG. 11 is a schematic illustration of the exhaust valve rocker arm assembly of FIG. 10;
FIG. 12 is a side view of the exhaust valve rocker arm assembly shown with the exhaust rocker arm on maximum lift and the engine brake rocker arm on the base circle of the cam shaft;
FIG. 13 is a schematic illustration of the exhaust valve rocker arm assembly of FIG. 12;
FIG. 14 is a side view of the exhaust valve rocker arm assembly shown with the exhaust rocker arm and the engine brake rocker arm on the base circle of the cam shaft;
FIG. 15 is a schematic illustration of the exhaust valve rocker arm assembly of FIG. 14;
FIG. 16 is a side view of the exhaust valve rocker arm assembly shown with the exhaust rocker arm on the base circle and the engine brake rocker arm rotated a distance counterclockwise from engaging a raised portion of the cam shaft;
FIG. 17 is a schematic illustration of the exhaust valve rocker arm assembly of FIG. 16;
FIG. 18 is a side view of the exhaust valve rocker arm assembly shown with the exhaust rocker arm at maximum lift and the engine brake rocker arm on the base circle of the cam shaft;
FIG. 19 is a schematic illustration of the exhaust valve rocker arm assembly of FIG. 18;
FIG. 20 is a side view of the exhaust valve rocker arm assembly shown with the exhaust rocker arm and the engine brake rocker arm on the base circle of the cam shaft; and
FIG. 21 is a schematic illustration of the exhaust valve rocker arm assembly of FIG. 20.

DETAILED DESCRIPTION

Heavy duty (HD) diesel engines with single overhead cam (SOHC) valvetrain 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 valvetrain (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.
With initial reference to FIG. 1, a partial valve train assembly constructed in accordance to one example of the present disclosure is shown and generally identified at reference 10. The partial valve train assembly 10 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. The partial valve train assembly 10 is supported in a valve train carrier 12 and can include three rocker arms per cylinder.
Specifically, each cylinder includes an intake valve rocker arm assembly 20, an exhaust valve rocker arm assembly 22 and an engine brake rocker arm assembly 24. The exhaust valve rocker arm assembly 22 and the engine brake rocker arm assembly 24 cooperate to control opening of the exhaust valves and are collectively referred to as a dual exhaust valve rocker arm assembly 26 (FIG. 2). The intake valve rocker arm assembly 20 is configured to control motion of the intake valves. The exhaust valve rocker arm assembly 22 is configured to control exhaust valve motion in a drive mode. The engine brake rocker arm assembly 24 is configured to act on one of the two exhaust arms in an engine brake mode as will be described herein. A rocker shaft 34 is received by the valve train carrier 12 and supports rotation of the exhaust valve rocker arm assembly 22 and the engine brake rocker arm assembly 24.
With further reference now to FIGS. 2 and 3, an exhaust valve rocker arm assembly 22 will be further described. The exhaust valve rocker arm assembly 22 can generally include an exhaust rocker arm 40, a valve bridge 42, a spigot spigot assembly 44 and an engine brake capsule 46. The valve bridge 42 engages a first and second exhaust valve 50 and 52 (FIG. 2) associated with a cylinder of an engine (not shown). The exhaust rocker arm 40 rotates around the rocker shaft 34 based on a lift profile of a cam shaft 54. The engine brake rocker arm assembly 24 can include an engine brake rocker arm 60 having an engaging portion 62. The engine brake rocker arm 60 rotates around the rocker shaft 34 based on a lift provide of the cam shaft 54.
With specific reference to FIG. 3, schematic function of the exhaust valve rocker arm assembly 22 and the engine brake rocker arm assembly 24 will be described. The configuration includes an oil control valve 70 that provides oil flow 72 for actuation from a pressurized oil supply 74. Pressurized oil chamber 78 is shown inside the engine brake capsule 46. The engine brake capsule 46 can include an engine brake capsule piston 80 and an engine brake capsule body 82. A valve tip pin 83 is positioned between the exhaust valve 52 and the engine brake capsule body 82. A c-clip 84 can provide a hard stop for the engine brake capsule body 82. An engine brake rocker arm schematic 90 represents the engine brake rocker arm assembly 24 rotating as a result of cam lobe breaking 92.
An actuator assembly 100 includes an actuator body 102, an actuator check ball 104, an actuator needle 106, an actuator return spring 108 and an actuator locking nut 110. When the engine is in drive (combustion) mode, the oil control valve 70 is closed and the engine brake capsule body 82 is completely retracted having no influence on the exhaust valves 50 and 52 motion. The actuator needle 106 can keep the check ball 104 in an open position (away from corresponding seat 107) and prevent oil pressure buildup in the engine brake capsule 46. The motion of the engine brake rocker arm 60 (FIG. 2), or represented in FIG. 3 as the rocker arm schematic 90 will have no effect on the motion of the exhaust valve 52 when the engine is in drive mode.
When the engine is in brake (no combustion) mode, the oil control valve 70 will be energized open and oil pressure will push back the actuator needle 106 and fill (extend) the engine brake capsule 46 for a predetermined length such as 4 mm. A gap between the engine brake rocker arm 60 (rocker arm schematic 90) and the exhaust valve 52 will be compensated so that motion of the engine brake rocker arm 60 controlled by the cam lobe 92 will create additional lift on the exhaust valve 52. The actuator check ball 104 will allow one-way oil replenishment at every cycle into the pressurized oil chamber 78. When de-energizing the oil control valve 70, the needle 106 will allow oil out from the pressurized oil chamber 78 and the engine brake capsule 46 will go back into a retracted position allowing driving mode (combustion) again. The engine brake rocker arm assembly 24 opens the exhaust valve 52 (positioned closer to the rocker shaft 34) providing favorable force ratio allowing higher braking power. The exhaust valve 52 is opened later in a compression stroke (close to top dead center), still with acceptable load on the cam lobe.
FIG. 4 illustrates the engine brake capsule 46 expanded or extended. The gap between the engine brake capsule body 82 and the valve tip pin 83 is eliminated. FIG. 5 illustrates the engine brake at maximum lift. The exhaust rocker arm 40 is on the base circle while the engine brake rocker arm 60 controls the lift of the engine brake exhaust valve 52. Explained further, the engine brake rocker arm 60 acts on the engine brake capsule piston 80, which acts on the engine brake capsule body 82, which acts on the valve tip pin 83, which acts on the engine brake exhaust valve 52.
With reference now to FIGS. 6 and 7, additional features of the present disclosure will be described. A ball lock assembly 150 includes a ball lock 152 and a ball lock spring 154. The ball lock spring 154 urges (identified by force F, FIG. 7) the ball lock 152 into a groove 160 defined on the outer diameter of the engine brake capsule body 82. The groove 160 has a depth 170 and a radius 172 configured to assure the engine brake capsule body 82 does not shake by its inertia, but rather under the load of the engine brake rocker arm 60 in engine brake mode. The ball lock assembly 150 will have no impact on the engine brake capsule piston 80 expansion or retraction time. A c-clip 180 is provided to limit the stroke of the engine brake capsule body 82. In this regard, the c-clip 180 provides a hard stop important for transportation.
Turning now to FIGS. 8 and 9, additional features will be described. A first adjustment screw 210 is provided on the engine brake arm 60. A second adjustment screw 212 is provided on the exhaust arm 40. A third adjustment screw 214 is provided on the intake arm 20. Each of the first, second and third adjustment screws 210, 212 and 214 all provide valve lash settings according to one example of the present disclosure. To set the engine brake lash, the engine brake capsule 46 is pushed down (as viewed in FIG. 9) into the collapsed position (no oil) to zero the lash in the exhaust valve 52. From this position, the first adjustment screw 210 is re-winded for exhaust brake capsule stroke and lash on the same valve. In one example the engine brake capsule 46 is made such that the difference between a fully collapsed and fully expanded length is within a narrow tolerance 220 (such as plus or minus 0.05 mm). Each of the first, second and third adjustment screws 210, 212 and 214 can have a common thread and nut size so that a common tool can be used for adjustment.
The present configuration provides many benefits. For example, actuation of engine brake function is controlled by pressurized engine oil by two oil control valves 70, one for each of the three cylinders (for the example shown in FIG. 1). The oil control valves 70 can be configured to operate independently. Valve actuation components for three cylinders are incorporated in one valvetrain carrier 12 ready to be assembled on a cylinder head. The configuration provides high performance engine braking without necessarily creating high load on valvetrain components by acting solely on one exhaust valve 52. By using a dedicated rocker arm (engine brake rocker arm 60), for engine brake, favorable rocker and force ratio transmitting lower load on the rocker shaft 34 and camshaft 54.
Furthermore, the engine brake capsule 46 is installed in and guided by an inner diameter 190 (FIG. 6) defined in the exhaust rocker arm 40. In this regard, while prior art configurations may provide a hydraulic capsule configured within the engine brake rocker arm, the present disclosure includes an engine brake capsule 46 configured in the exhaust rocker arm 40 (instead of in the engine brake rocker arm 60). The configuration provides favorable packaging advantages. The engine brake capsule 46 is configured to move freely along the inner diameter 190 in the exhaust rocker arm 40 while being controlled by the engine brake rocker arm 60.
The configuration of the present disclosure provides actuation control from the actuator assembly 100 to move the engine brake capsule 46 between an extended and retracted position. The actuator assembly 100 and the oil control valve 70 (FIG. 3) are configured in the exhaust rocker arm 40 and are separate from the engine brake capsule 46. Moreover, the ball lock assembly 150 provides drive mode retention of the engine brake capsule body 82 in drive mode.
With reference now to FIGS. 10-21, an exemplary operating sequence of the dual exhaust valve rocker arm assembly 26 will be described. FIG. 10 shows the exhaust rocker arm 40 and the engine brake rocker arm 60 on the base circle of the cam shaft 54. The engaging portion 62 of the engine brake engine brake rocker arm 60 is disengaged with the engine brake capsule piston 80. The engine brake capsule 46 is collapsed. The schematic of FIG. 11 corresponds to the position of the dual exhaust valve rocker arm assembly 26 in FIG. 10. The oil control valve 70 is closed draining open. The check ball 104 is in an open position away from its seat 107.
FIGS. 12 and 13 will now be described. FIG. 12 shows the exhaust rocker arm 40 on maximum lift of the cam shaft 54 and the engine brake rocker arm 60 on the base circle of the cam shaft 54. The engaging portion 62 of the engine brake rocker arm 60 is disengaged with the engine brake capsule piston 80. An exhaust brake rocker arm lost motion spring 232 keeps the engine brake rocker arm 60 against the camshaft 54. The engine brake capsule 46 is collapsed. The schematic of FIG. 13 corresponds to the position of the dual exhaust valve rocker arm assembly 26 in FIG. 12. The oil control valve 70 is closed draining open. The check ball 104 is in an open position away from its seat 107.
FIGS. 14 and 15 will now be described. FIG. 14 shows the exhaust rocker arm 40 on the base circle of the cam shaft 54 and the engine brake rocker arm 60 on the base circle of the cam shaft 54. The engaging portion 62 of the engine brake rocker arm 60 is engaged with the engine brake capsule piston 80. The engine brake capsule 46 is expanded such that engine brake capsule body 82 touches the valve tip 83 on the valve bridge 42. The schematic of FIG. 15 corresponds to the position of the dual exhaust valve rocker arm assembly 26 in FIG. 14. The oil control valve 70 is open. The needle 106 is retracted. The check ball 104 opens only under oil pressure from the oil control valve 70.
FIGS. 16 and 17 will now be described. FIG. 16 shows the exhaust rocker arm 40 on the base circle of the cam shaft 54 and the engine brake rocker arm 60 rotated a distance counterclockwise from engaging a raised portion of the cam shaft 54. The engaging portion 62 of the engine brake rocker arm 60 is engaged with the engine brake capsule piston 80. The engine brake capsule 46 is expanded such that engine brake capsule body 82 touches the valve tip 83 on the valve bridge 42. Rigid transitioning of the engine brake rocker arm 60 motion to the exhaust valve 52 engine brake lift (opening) is shown. The schematic of FIG. 17 corresponds to the position of the dual exhaust valve rocker arm assembly 26 in FIG. 16. The oil control valve 70 is open. The needle 106 is retracted. The check ball 104 is closed by pressure from the engine brake capsule 46.
FIGS. 18 and 19 will now be described. FIG. 18 shows the exhaust rocker arm 40 at maximum lift on cam shaft 54 and the engine brake rocker arm 60 on the base circle of the cam shaft 54. Once passed the engine brake lift, the exhaust rocker arm assembly 22 will control opening of both valves 50, 52. The engine brake rocker arm 60 will be kept in place against the cam shaft 54 by the lost motion spring 232. The schematic of FIG. 19 corresponds to the position of the dual exhaust valve rocker arm assembly 26 in FIG. 18. The oil control valve 70 is open. The needle 106 is retracted. The check ball 104 opens only by pressure from the engine brake capsule 46. The engine brake capsule 46 will expand up to its hard stop for maximum extension.
FIGS. 20 and 21 will now be described. FIG. 20 shows the exhaust rocker arm 40 and the engine brake rocker arm 60 on the base circle of the cam shaft 54. Both exhaust valves 50, 52 will close contemporary controlled by the exhaust rocker arm assembly 22. The engine brake capsule 46 will be (again) fully expanded. Oil leaked out from the engine brake capsule 46 during the lift will be replenished. The schematic of FIG. 21 corresponds to the position of the dual exhaust valve rocker arm assembly 26 in FIG. 20. The oil control valve 70 is open. The needle 106 is retracted. The check ball 104 opens only by pressure from the engine brake capsule 46. The engine brake capsule 46 will expand up to its hard stop for maximum extension.

Claims

A dual exhaust valve rocker arm assembly (26) operable in a combustion engine mode and an engine braking mode, the dual exhaust valve rocker arm assembly (26) selectively opening first and second exhaust valves (50, 52) and comprising:
a rocker shaft (34);

an exhaust valve rocker arm assembly (22) having an exhaust rocker arm (40) that receives the rocker shaft (34) and is configured to rotate around the rocker shaft (34), the exhaust rocker arm further (40) defining a bore having an inner diameter (190);

an engine brake rocker arm assembly (24) having an engine brake rocker arm (60); and

an engine brake capsule (46) slidably received along the inner diameter (190) of the bore of the exhaust valve rocker arm (40), wherein the engine brake capsule (46) includes an engine brake capsule piston (80) and an engine brake capsule body (82), wherein a pressurized oil chamber (78) is defined between the engine brake capsule piston (80) and the engine brake capsule body (82), wherein the engine brake rocker arm (60) is configured to act on the engine brake capsule piston (80) which acts on the engine brake capsule body (82) which ultimately acts on one of the first and second exhaust valves (50, 52), and wherein the engine brake capsule (46) is selectively translatable upon urging by the engine brake rocker arm- (60), the engine brake capsule (46), in turn, urging one of the first and second exhaust valves (50, 52) open during engine braking mode;

wherein the dual exhaust valve rocker arm assembly further comprises:
an oil control valve (70) that provides oil flow for actuation of the engine brake capsule (46) from a pressurized oil supply (74),

characterized in that:
the dual exhaust valve rocker arm assembly (26) comprises:
a lock ball assembly (150) including a ball lock (152) and a ball lock spring (154);

wherein the ball lock spring (154) of the lock ball assembly (150) is configured to urge the ball lock (152) into a groove (160) defined on the engine brake capsule body (82) to provide retention of the engine brake capsule body (82) in the combustion mode;

wherein, when the engine is in the combustion mode, the oil control valve (70) is closed and the engine brake capsule body (82) is completely retracted having no influence on the first and second exhaust valves (50, 52) motion and is retained by the lock ball assembly (150).
The dual exhaust valve rocker arm assembly of claim 1, further comprising a valve tip (83) positioned between one of the first and second exhaust valves (52) and the engine brake capsule body (82).
The dual exhaust valve rocker arm assembly of claim 1, further comprising a c-clip (84) configured on the rocker arm assembly and that limits a stroke of the engine brake capsule (46) and provides a hard stop.
The dual exhaust valve rocker arm assembly of claim 1, further comprising:
an actuator assembly configured to move the engine brake capsule (46) between an extended and a retracted position.
The dual exhaust valve rocker arm assembly of claim 4, wherein the actuator assembly (100) and the oil control valve (70) are configured in the exhaust rocker arm (40) separate from the engine brake capsule (46).
The dual exhaust valve rocker arm assembly of claim 4, wherein the actuator assembly (100) includes an actuator body (102), an actuator check ball (140), an actuator needle (106), an actuator return spring (108) and an actuator locking nut (110), wherein the actuator needle (106) is configured to keep the actuator check ball (140) in an open position and prevent oil pressure build-up in the engine brake capsule (46).
The dual exhaust valve rocker arm assembly of claim 6, wherein the actuator check ball allows (140) one-way replenishment at every cycle into the pressurized oil chamber (78).
The dual exhaust valve rocker arm assembly of claim 6, wherein in engine braking mode, the oil control valve (70) is energized open and oil pressure causes the actuator needle (106) to move away from a corresponding seat (107) such that the engine brake capsule (46) is extended a predetermined length.
The dual exhaust valve rocker arm assembly of claim 8, wherein de-energizing the oil control valve (70) causes the actuator needle (106) to allow oil out from the pressurized oil chamber (78) and the engine brake capsule (46) to move to the retracted position allowing combustion.
The dual exhaust valve rocker arm assembly of claim 1, further comprising:
a first adjustment screw provided (210) on the engine brake rocker arm (60); and

a second adjustment screw (212) provided on the exhaust rocker arm (40); wherein both of the first and second adjustment screws (210, 212) are adjustably positioned to selectively provide lash settings for the dual exhaust rocker arm assembly.