Patent Publication Number: US-11377985-B2

Title: Switching tappet or a roller finger follower for compression release braking

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of International Patent Application No. PCT/US18/49370 filed on Sep. 4, 2018, claims the benefit of the filing date of U.S. Provisional Application No. 62/561,771 filed on Sep. 22, 2017, which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to operation of an internal combustion engine system, and more particularly, but not exclusively, relates to a switching tappet and a roller finger follower for compression release braking of an internal combustion engine. 
     Various engine braking systems have been developed to provide compression release braking of an internal combustion engine. One form of an engine braking system is a compression release engine brake. When the compression release engine brake is activated, it opens exhaust valves in the cylinders after the compression cycle, releasing the compressed air trapped in the cylinders, and slowing the vehicle. However, a compression release engine brake is sensitive and often hard to implement, maintain, or install properly. Moreover, compression release engine brakes are expensive. 
     However, further contributions in this area of technology are needed to provide improved compression release braking and control for certain types of valvetrains. Further contributions are needed to provide improved compression release for a lower cost. 
     SUMMARY 
     Certain embodiments of the present application includes unique systems, methods and apparatus for operation of an internal combustion engine using an engine braking system for compression release braking. In a unique system, a switching tappet includes an inner tappet and an outer tappet that are selectively controlled to cooperate with inner and outer cam lobes for exhaust release (braking) during the exhaust stoke and compression release during the compression stroke. In another unique system, a roller finger follower is selectively controlled to cooperate with inner and outer cam lobes for exhaust release (braking) during the exhaust stoke and compression release during the compression stroke. Other embodiments include unique apparatus, devices, systems, and methods involving the control of an internal combustion engine system via an engine braking system to meet one or more of an engine braking request and a vehicle or engine speed request. Either of these embodiments can also be used for a compression release event. The compression release event can be changed to a compression brake event with a camshaft phaser to move the exhaust brake event to a power stroke rather than the compression stroke. Moreover, a default position of either valvetrain is to provide compression release event. No system response is required during cranking or starting of the engine. These systems are capable of compression braking when the exhaust event is positioned during the exhaust stroke to release gas and as a compression release when positioned on the compression stroke. When the gas release occurs on the power stroke there is a braking function. When the gas release occurs on the compression stroke there is a lower power starting situation. 
     This summary is provided to introduce a selection of concepts that are further described below in the illustrative embodiments. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic view of one embodiment of an internal combustion engine system operable to provide compression release braking. 
         FIG. 2  is a diagrammatic and schematic view of one embodiment of a cylinder of the internal combustion engine system of  FIG. 1  and a schematic of a valve actuation mechanism. 
         FIG. 3  is a perspective view showing a prior art non-switching flat tappet part of a valve train of the internal combustion engine for intake or exhaust valve actuation. 
         FIG. 4  is a perspective view in partial section of a switching tappet part of a valve train. 
         FIG. 5  is a graph showing a relationship between crank angle and intake and exhaust valve lift profiles for a variable valve lift cam lobe. 
         FIGS. 6A-6E  are a series of graphs showing various intake and exhaust valve lift profiles during a normal (non-braking) mode and an exhaust valve lift during a braking mode. 
         FIG. 7  is a graph of nominal lift profiles and compression brake profiles. 
         FIG. 8  is a diagrammatic and schematic view of a second embodiment of a cylinder of the internal combustion engine system of  FIG. 1  and a schematic of a second embodiment of a roller finger follower. 
         FIG. 9  is a perspective view of the roller finger follower from  FIG. 8 . 
         FIG. 10  is a perspective view of the roller finger follower from  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS 
     While the present invention can take many different forms, for the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
     With reference to  FIG. 1 , an internal combustion engine system  10  includes a four-stroke internal combustion engine  12 .  FIG. 1  illustrates an embodiment where the engine  12  is a diesel engine, but any engine type is contemplated, including compression ignition, spark-ignition, and combinations of these. The engine  12  can include a plurality of cylinders  14 .  FIG. 1  illustrates the plurality of cylinders  14  in an arrangement that includes six cylinders  14  in an in-line arrangement for illustration purposes only. Any number of cylinders and any arrangement of the cylinders suitable for use in an internal combustion engine can be utilized. The number of cylinders  14  that can be used can range from one cylinder to eighteen or more. Furthermore, the following description at times will be in reference to one of the cylinders  14 . It is to be realized that corresponding features in reference to the cylinder  14  described in  FIG. 2  and at other locations herein can be present for all or a subset of the other cylinders  14  of engine  12 . 
     As shown in  FIG. 2 , the cylinder  14  houses a piston  16  that is operably attached to a crankshaft  18  that is rotated by reciprocal movement of piston  16  in a combustion chamber  28  of the cylinder  14 . Within a cylinder head  20  of the cylinder  14 , there is at least one intake valve  22 , at least one exhaust valve  24 , and a fuel injector  26  that provides fuel to the combustion chamber  28  formed by cylinder  14  between the piston  16  and the cylinder head  20 . In other embodiments, fuel can be provided to combustion chamber  28  by port injection, or by injection in the intake system, upstream of combustion chamber  28 . 
     The term “four-stroke” herein means the following four strokes—intake, compression, power, and exhaust—that the piston  16  completes during two separate revolutions of the engine&#39;s crankshaft  18 . A stroke begins either at a top dead center (TDC) when the piston  16  is at the top of cylinder head  20  of the cylinder  14 , or at a bottom dead center (BDC), when the piston  16  has reached its lowest point in the cylinder  14 . 
     During the intake stroke, the piston  16  descends away from cylinder head  20  of the cylinder  14  to a bottom (not shown) of the cylinder, thereby reducing the pressure in the combustion chamber  28  of the cylinder  14 . In the instance where the engine  12  is a diesel engine, a combustion charge is created in the combustion chamber  28  by an intake of air through the intake valve  22  when the intake valve  22  is opened. 
     The fuel from the fuel injector  26  is supplied by a high pressure common-rail system  30  ( FIG. 1 ) that is connected to the fuel tank  32 . Fuel from the fuel tank  32  is suctioned by a fuel pump (not shown) and fed to the common-rail fuel system  30 . The fuel fed from the fuel pump is accumulated in the common-rail fuel system  30 , and the accumulated fuel is supplied to the fuel injector  26  of each cylinder  14  through a fuel line  34 . The accumulated fuel in common rail system can be pressurized to boost and control the fuel pressure of the fuel delivered to combustion chamber  28  of each cylinder  14 . 
     During the compression stroke in a non-engine braking mode of operation, both the intake valve  22  and the exhaust valve  24  are closed. The piston  16  returns toward TDC and fuel is injected near TDC in the compressed air in a main injection event, and the compressed fuel-air mixture ignites in the combustion chamber  28  after a short delay. In the instance where the engine  12  is a diesel engine, this results in the combustion charge being ignited. The ignition of the air and fuel causes a rapid increase in pressure in the combustion chamber  28 , which is applied to the piston  16  during its power stroke toward the BDC. Combustion phasing in combustion chamber  28  is calibrated so that the increase in pressure in combustion chamber  28  pushes piston  16 , providing a net positive in the force/work/power of piston  16 . 
     During the exhaust stroke, the piston  16  is returned toward TDC while the exhaust valve  24  is open. This action discharges the burnt products of the combustion of the fuel in the combustion chamber  28  and expels the spent fuel-air mixture (exhaust gas) out through the exhaust valve  24 . 
     The intake air flows through an intake passage  36  and intake manifold  38  before reaching the intake valve  22 . The intake passage  36  may be connected to a compressor  40   a  of a turbocharger  40  and an optional intake air throttle  42 . The intake air can be purified by an air cleaner (not shown), compressed by the compressor  40   a  and then aspirated into the combustion chamber  28  through the intake air throttle  42 . The intake air throttle  42  can be controlled to influence the air flow into the cylinder. Embodiments without turbocharger  40  are also contemplated. 
     The intake passage  36  can be further provided with a cooler  44  that is provided downstream of the compressor  40   a . In one example, the cooler  44  can be a charge air cooler (CAC). In this example, the compressor  40   a  can increase the temperature and pressure of the intake air, while the CAC  44  can increase a charge density and provide more air to the cylinders. In another example, the cooler  44  can be a low temperature aftercooler (LTA). The CAC  44  uses air as the cooling media, while the LTA uses coolant as the cooling media. 
     The exhaust gas flows out from the combustion chamber  28  into an exhaust passage  46  from an exhaust manifold  48  that connects the cylinders  14  to exhaust passage  46 . The exhaust passage  46  is connected to a turbine  40   b  and a wastegate  50  of the turbocharger  40  and then into an aftertreatment system  52 . The exhaust gas that is discharged from the combustion chamber  28  drives the turbine  40   b  to rotate. The wastegate  50  is a device that enables part of the exhaust gas to by-pass the turbine  40   b  through a passageway  54 . Less exhaust gas energy is thereby available to the turbine  40   b , leading to less power transfer to the compressor  40   a . Typically, this leads to reduced intake air pressure rise across the compressor  40   a  and lower intake air density/flow. The wastegate  50  can include a control valve  56  that can be an open/closed (two position) type of valve, or a full authority valve allowing control over the amount of by-pass flow, or anything between. The exhaust passage  46  can further or alternatively include an exhaust throttle  58  for adjusting the flow of the exhaust gas through the exhaust passage  46 . The exhaust gas, which can be a combination of by-passed and turbine flow, then enters the aftertreatment system  52 . 
     Optionally, a part of the exhaust gas can be recirculated into the intake system via an EGR passage (not shown.) The EGR passage can be connected the exhaust passage upstream of the turbine  40   b  to the intake passage  36  downstream of the intake air throttle  42 . Alternatively or additionally, a low pressure EGR system (not shown) can be provided downstream of turbine  40   b  and upstream of compressor  40   a . An EGR valve can be provided for regulating the EGR flow through the EGR passage. The EGR passage can be further provided with an EGR cooler and a bypass around the EGR cooler. 
     The aftertreatment system  52  may include one or more devices useful for handling and/or removing material from exhaust gas that may be harmful constituents, including carbon monoxide, nitric oxide, nitrogen dioxide, hydrocarbons, and/or soot in the exhaust gas. In some examples, the aftertreatment system  52  can include at least one of a catalytic device and a particulate matter filter. The catalytic device can be a diesel oxidation catalyst (DOC) device, ammonia oxidation (AMOX) catalyst device, a selective catalytic reduction (SCR) device, three-way catalyst (TWC), lean NOX trap (LNT) etc. The reduction catalyst can include any suitable reduction catalysts, for example, a urea selective reduction catalyst. The particulate matter filter can be a diesel particulate filter (DPF), a partial flow particulate filter (PFF), etc. A PFF functions to capture the particulate matter in a portion of the flow; in contrast the entire exhaust gas volume passes through the particulate filter. 
     The arrangement of the components in the aftertreatment system  52  can be any arrangement that is suitable for use with the engine  12 . For example, in one embodiment, a DOC and a DPF are provided upstream of a SCR device. In one example, a reductant delivery device is provided between the DPF and the SCR device for injecting a reductant into the exhaust gas upstream of SCR device. The reductant can be urea, diesel exhaust fluid, or any suitable reductant injected in liquid and/or gaseous form. 
     A controller  80  is provided to receive data as input from various sensors, and send command signals as output to various actuators. Some of the various sensors and actuators that may be employed are described in detail below. The controller  80  can include, for example, a processor, a memory, a clock, and an input/output (I/O) interface. 
     The system  10  may include various sensors such as an intake manifold pressure/temperature sensor  70 , an exhaust manifold pressure/temperature sensor  72 , one or more aftertreatment sensors  74  (such as a differential pressure sensor, temperature sensor(s), pressure sensor(s), constituent sensor(s)), engine sensors  76  (which can detect the air/fuel ratio of the air/fuel mixture supplied to the combustion chamber, a crank angle, the rotation speed of the crankshaft, etc.), and a fuel sensor  78  to detect the fuel pressure and/or other properties of the fuel, common rail  38  and/or fuel injector  26 . Any other sensors known in the art for an engine system are also contemplated. 
     System  10  can also include various actuators for opening and closing the intake valves  22 , for opening and closing the exhaust valves  24 , for injecting fuel from the fuel injector  26 , for opening and closing the wastegate valve  56 , for the intake air throttle  42 , and/or for the exhaust throttle  58 . The actuators are not illustrated in  FIG. 1 , but one skilled in the art would know how to implement the mechanism needed for each of the components to perform the intended function. Furthermore, in one embodiment, the actuators for opening and closing the intake and exhaust valves  22 ,  24  is a valve actuation (VA) system  90 , such as a variable valve actuation mechanism. 
     Referring to  FIG. 3 , there is shown a prior art non-switching type of tappet  100 ′ that includes a flat upper surface  102 ′. In contrast,  FIG. 4  provides further details regarding one embodiment of a switching tappet  100  for VA system  90  is shown that is applicable to compression release braking in conjunction with VA technology. Specifically, the VA system  90  includes compression release brake lobes that are coupled to one or more camshafts (not shown) that are in contact with or contactable with switching tappet  100 . The VA system  90  can further include a phaser that adjusts a relative positioning and timing of the compression release brake lobes during engine braking operations. The switching tappet  100  is connected to an exhaust valve  24  so that the cam lobe or lobes acting on switching tappet  100  open and close the connected exhaust valve during rotation of the camshaft. 
     Switching tappet  100  can be employed in a type-1 valvetrain (DOHC with direct-acting tappet) that operates the intake and exhaust valves  22 ,  24  via a camshaft having a number of cam lobes. In certain embodiments, switching tappet  100  is a bucket type tappet that includes an inner bucket shaped member  104  that is surrounded by an outer member  106 . The switching tappet  100  also includes a contoured contact surface  102  defined in part by the inner member  104  and outer member  106  so that at least a part of the contact surface  102  maintains a sliding contact with one or more cam lobes and opens the respective valve  22 ,  24  according to the lift profile via a direct tappet-valve surface contact. To implement compression braking with switching tappet  100 , the system is required to actuate an additional lift profile (corresponding to a compression brake) as and when required during engine operation, such as shown in  FIG. 6E . To implement a compression brake event with switching tappet  100 , the system is required to actuate an additional lift profile  301  (corresponding to a compression brake) as and when required during engine operation, such as shown in  FIG. 7 .  FIG. 7  illustrates an exemplary nominal intake valve lift profile  3001  and an exemplary nominal exhaust valve lift profile  300 E. 
     In one embodiment, switching tappet  100  is implemented in a VA system  90  that provides variable valve lift (VVL). For VVL, each valve is served by three cam lobes where the center cam lobe has lower lift and shorter duration and the outer two are identical with higher lift and longer duration. The switching tappet  100  includes inner tappet  104  for contacting the center cam lobe and a concentric outer ring-shaped tappet  106  for contacting the outer two cam lobes. Inner tappet  104  can be locked together with outer tappet  106  by a locking mechanism such as a hydraulically operated locking pin  108 . 
     The selection of the cam lobe against which the switching tappet  100  acts during engine operation is made by the controller  80 . Controller  80  is configured to provide a command to activate the hydraulic locking pin  108  to engage the outer tappet  106  with inner tappet  104  and in turn, the higher lift profile cam lobe, as and when required. The inner tappet  104  moves freely under the shadow of the outer tappet&#39;s  106  higher lift profile. When the tappets  104 ,  106  are not locked together, the exhaust valve  24  is actuated by the low cam lobe via the inner tappet  104  and the outer tappet  106  moves independently of the valve motion ( FIG. 5 ). This configuration can also be used to implement cylinder de-activation (CDA) by just reducing the inner cam lobe profile to the base circle so that zero lift is achieved via the inner tappet  104  when CDA is activated. 
     To achieve compression braking with switching tappet  100 , the lower braking lift profile is to be pushed out of the shadow of the higher nominal lift profile, as shown in  FIG. 5  and  FIGS. 6A-6E . This is a result of the performance requirement to release compressed air in the cylinder  14  just as the compression stroke ends. Hence, during compression release engine braking, the exhaust valve  24  is required to operate on both lift profiles (nominal and compression release). Since, the switching tappet  100  limits the switching option to only the outer tappet  106 , the engine braking lift profile is placed on the outer lobes of the cam in contact with outer tappet  106 . The inner cam lobe is always engaged with the inner tappet  104  to satisfy the exhaust lift event requirements. 
     When the braking command is received, controller  80  activates the hydraulic locking pin  108  which locks the outer tappet  106  and the inner tappet  104 . Thus, during the braking mode, both cam lobes would be engaged with the valve through switching tappet  100  thereby obtaining the desired valve lift profiles for compression braking and compression release. 
       FIG. 7  also illustrates an exemplary compression braking profile  301  for operation of exhaust valve(s)  24 . Also illustrated is a nominal lift profile, such as for example, nominal lift profiles  300 E and  3001  shown in  FIG. 7 . As discussed above, the switching tappet  100  can be employed in a type-1 valvetrain or the VA system  90  and is based on a compression brake and compression release valve profile, such as, for example, shown in  FIG. 7 . Alternatively, the compression brake is achieved in one embodiment by the use of the profile switching valvetrain. The compression brake profile is offset significantly from the normal exhaust profile and has a shorter peak lift. The compression brake profile is shifted such that it starts to open shortly around TDC of the compression stroke or TDC of the power stroke (fuel or no fuel). This same profile may be used in combination with a cam phaser to move the profile to a compression stroke side of TDC to provide a compression release function. One example of the cam phaser is a gear system attached to the internal combustion engine  12  that is configured to adjust the cam shaft position while the engine is running wherein the cam phaser is operably controlled by the controller  80 . Due to the short peak lift of the exhaust brake profile, piston and head design may be made to accommodate this lift profile at peak lift at TDC. If the crank angle is less than zero degrees, then the cam phaser reduces the compression event and reduces the power required to start engine  12 . If the crank angle is greater than zero degrees, then more power is sent to the engine  12  and a compression braking event occurs. 
     During operation of the internal combustion engine system  10 , the controller  80  can receive information from the various sensors listed above through I/O interface(s), process the received information using a processor based on an algorithm stored in a memory of the controller  80 , and then send command signals to the various actuators through the I/O interface. For example, the controller  80  can receive information regarding an engine braking request, a vehicle or engine speed request, and/or one or more temperature inputs regarding a thermal management condition. The controller  80  is configured to process the requests and/or temperature input(s), and then based on the control strategy, send one or more command signals to one or more actuators to provide engine braking locking tappets  104 ,  106  to one another and modulate an opening/closing timing of the exhaust valve(s)  24  using the associated engine braking cam lobe(s). 
     The controller  80  can be configured to implement the disclosed combustion and thermal management strategies using VA system  90  and fuel system  30 . In one embodiment, the disclosed method and/or controller configuration include the controller  80  providing an engine braking command in response to an engine braking request that is based on one or more signals from one or more of the plurality of sensors described above for internal combustion engine system  10 . The engine braking command controls VA mechanism  90  to provide a braking power with the engine  12  at a given engine speed by modulating a timing of at least one of an exhaust valve opening and an exhaust valve closing during a compression stroke of the piston(s)  16  of engine  12 . 
     The control procedures implemented by the controller  80  can be executed by a processor of controller  80  executing program instructions (algorithms) stored in the memory of the controller  80 . The descriptions herein can be implemented with internal combustion engine system  10 . In certain embodiments, the internal combustion engine system  10  further includes a controller  80  structured or configured to perform certain operations to control internal combustion engine system  10  in achieving one or more target conditions. In certain embodiments, the controller forms a portion of a processing subsystem including one or more computing devices having memory, processing, and communication hardware. The controller may be a single device or a distributed device, and the functions of the controller  80  may be performed by hardware and/or by instructions encoded on a computer readable medium. 
     In certain embodiments, the controller  80  includes one or more modules structured to functionally execute the operations of the controller. The description herein including modules emphasizes the structural independence of the aspects of the controller, and illustrates one grouping of operations and responsibilities of the controller. Other groupings that execute similar overall operations are understood within the scope of the present application. Modules may be implemented in hardware and/or software on a non-transient computer readable storage medium, and modules may be distributed across various hardware or other computer components. 
     Certain operations described herein include operations to interpret or determine one or more parameters. Interpreting or determining, as utilized herein, includes receiving values by any method known in the art, including at least receiving values from a datalink or network communication, receiving an electronic signal (e.g. a voltage, frequency, current, or PWM signal) indicative of the value, receiving a software parameter indicative of the value, reading the value from a memory location on a non-transient computer readable storage medium, receiving the value as a run-time parameter by any means known in the art, and/or by receiving a value by which the interpreted or determined parameter can be calculated, and/or by referencing a default value that is interpreted or determined to be the parameter value. 
     The present disclosure is also applicable to a type-2 roller finger follower system or roller finger follower  800  utilized with an internal combustion engine system  10 ′ as illustrated in  FIGS. 8, 9, and 10 . The internal combustion engine system  10 ′ is similar to the internal combustion engine system  10  from  FIG. 1  in all aspects unless noted otherwise. The internal combustion engine system  10 ′ includes an intake valve  22 ′ similar to intake valve  22  from  FIG. 1 , and an exhaust valve  24 ′ similar to exhaust valve  24 . The roller finger follower  800  is utilized with a cam  1014  that includes one or more cam lobes that are in contact with the roller finger follower  800  as described in more detail below. 
     The roller finger follower  800  actuates intake and exhaust valves and provides for service needs, variable valve lift (VVL) or cylinder deactivation (CDA), and compression release brake needs. VVL and cylinder deactivation functionality is achieved in the type-2 roller finger follower system  800  with the use of a hydraulically operated pin or other locking mechanism.  FIGS. 8, 9, and 10  illustrate an exemplary type-2 roller finger follower  800  by way of example only and it will be appreciated that the configuration of the roller finger follower  800  is not limited to the configuration illustrated. 
     The roller finger follower  800  includes an outer sliding follower  803  and an inner roller follower arm  808  operatively connected by a hydraulic locking pin  810 . The outer sliding follower  803  includes a first outer arm or first outer sliding follower  804  opposite a second outer arm or second outer sliding follower  806 . In an assembled configuration, the inner roller follower arm  808  is sandwiched or disposed between the first and second outer sliding followers  804  and  806 . The first outer sliding follower  804 , the second outer sliding follower  806 , and the inner roller follower arm  808  are assembled together at a pivot axle (not illustrated). The pivot axle allows a rotational degree of freedom pivoting about the axle when the roller finger follower  800  is in a deactivated state. 
     The inner roller follower arm  808  includes a bearing  816  that includes a roller  818  that is mounted between a first inner side arm  820  and a second inner side arm  822  on a bearing axle (not illustrated) that during normal operation of the roller finger follower  800 , serves to transfer energy from a rotating cam (not illustrated) to the roller finger follower  800 . Mounting the roller  818  on the bearing axle allows the bearing  816  to rotate about the bearing axle, which serves to reduce the friction generated by the contact of the rotating cam with the roller  818 . As discussed herein, the roller  818  is rotatably secured to the first and second inner side arms  820  and  822 , which in turn may rotate relative to the first and second outer arms  804  and  806  about the pivot axle  812  under certain conditions. 
     As shown in  FIG. 10 , an intake valve  22 ′ is also in contact with the roller finger follower  800  near its first end  801 , and thus the reduced mass at the first end  101  of the roller finger follower  800  reduces the mass of the overall valve train (not shown), thereby reducing the force necessary to change the velocity of the valve train. 
     With continued reference to  FIG. 9 , the first outer arm  804  has a first lobe contacting surface  824  and the second outer arm  806  has a second lobe contacting surface  826 . The first and second lobe contacting surfaces  824 ,  826  are configured to come into contact with a first and a second cam lobe  1010 ,  1012  of a cam  1014 , as described in more detail below. 
     The mechanism for selectively deactivating the roller finger follower  800  is the hydraulic locking pin  810 . The hydraulic locking pin  810  is operated by the controller  80  that is configured to provide a command to activate the hydraulic locking pin  810  to engage the outer sliding follower  803  and in turn, a higher lift profile, as and when required. The inner roller follower arm  808  moves freely as its lift under the shadow of the outer sliding follower  803  higher lift profile. When the outer sliding follower  803  is not locked with the inner roller follower arm  808 , the valve is actuated by the low cam lobe via the inner roller follower arm  808  and the outer sliding follower  803  that move independent of the valve motion. This configuration can be used to implement CDA by reducing the outer cam lobe profile to the base circle or removing the outer lobes altogether so that zero lift is achieved via the outer sliding follower  803  when CDA is activated. 
       FIG. 10  illustrates a perspective front view of the roller finger follower  800  in relation to the cam  1014  having a center lift lobe  1020  configured to engage the inner roller follower arm  808 . The center lift lobe  1020  has a lower lift and shorter duration than the first and second cam lobes  1010 ,  1012 . The first and second cam lobes  1010 ,  1012  are identical to each other and have a higher lift and longer duration as compared to the center lift lobe  1020 . The first and second cam lobes  1010 ,  1012  each include a base circle  1022  and a lifting portion  1024  positioned above the first and second lobe contacting surfaces  824 ,  826 . The center lift lobe  1020  includes a base circle  1028  having a diameter that corresponds to the diameter of the base circle  1022 . It should be noted that the diameter of the base circle  1028  need not be identical to the diameter of the base circle  1022 , but may have a diameter equal to, smaller, or larger than the diameter of the base circle  1022 . In other embodiments, the first and second cam lobes  1010 ,  1012  and the center lift lobe  1020  may be configured differently. 
       FIGS. 8 and 10  illustrate the roller finger follower  800  assembled with the cam  1014 . A lash adjuster  1040  engages the roller finger follower  800  adjacent its second end  805 , and applies upward pressure to the roller finger follower  800 , and in particular the outer sliding follower  803 , while mitigating against valve lash. The valve stem  1002  engages the first end  801  of the roller finger follower  800 . In the activated state, the roller finger follower  800  periodically pushes the valve stem  102  downward, which serves to open the intake valve  22 ′. 
     During engine operation the selection of the cam lobe against which the roller finger follower  800  acts is made by the controller  80 . Controller  80  is configured to provide a command to activate the hydraulic locking pin  810  to engage the outer sliding follower  803  and in turn the higher lift profile cam lobe or the first and second cam lobes  1010 ,  1012 , as and when required. The inner roller follower arm  808  moves freely as its lift under the shadow of the outer sliding follower  803  higher lift profile. When the inner roller follower arm  808  and the outer sliding follower  803  are not locked together, the exhaust valve  24 ′ is actuated by the low cam lobe via the inner roller follower arm  808 , and the outer sliding follower  803  moves independently of the valve motion ( FIG. 5 ). This configuration can also be used to implement cylinder de-activation (CDA) by just reducing the outer cam lobe profile to the base circle or removing the outer lobes altogether so that zero lift is achieved via the outer sliding follower  803  when CDA is activated. 
     To achieve compression braking with the roller finger follower  800 , the lower braking profile is desired to be pushed out of the shadow of the higher nominal lift profile, as shown in  FIG. 5  and  FIGS. 6A-6E . This is a result of the performance requirement to release compressed air in the cylinder  14  just as the compression stroke ends. Hence, during compression release engine braking, the exhaust valve  24 ′ is required to operate on both lift profiles (nominal and compression release). Since, the roller finger follower  800  limits the switching option to only the outer sliding follower  803 , the braking lift profile would be placed on the outer lobes or the first and second cam lobes  1010 ,  1012  of the cam  1014 . The inner cam lobe or the center lift lobe  1020  would always remain engaged with the exhaust valve  24 ′ via the inner roller follower arm  808  to satisfy the exhaust lift event requirements. 
     When the braking command is received, the controller  80  activates the hydraulic locking pin  810  which locks the outer sliding follower  803  with the inner roller follower arm  808 . Thus, during the braking mode, both cam lobes would be engaged with the valve through the outer sliding follower  803  and the inner roller follower arm  808  thereby obtaining the desired valve lift profiles for compression braking and compression release. 
     As discussed above,  FIG. 7  illustrates an exemplary compression braking profile  301  for operation of exhaust valve(s)  24 , and a nominal lift profile, such as for example, nominal lift profiles  300 E and  3001 . The roller finger follower  800  can be employed in a type-2 valvetrain and operable with a compression brake and compression release valve profile, such as, for example, shown in  FIG. 7 . 
     As discussed above, either the switching tappet  100  employed in a type-1 valvetrain or the roller finger follower  800  in a type-2 valvetrain can be used for a compression release event or a compression braking event. In either configuration, a default position for the type-1 and type-2 valvetrains is a compression release event. 
     Various aspects of the present disclosure are contemplated. According to one aspect, a method, comprising receiving a charge flow into a plurality of cylinders of an internal combustion engine system from an intake system; opening an exhaust valve of one of the plurality of cylinders during an exhaust stroke of the cylinder with an inner member of a switching tappet acting on a first cam lobe of a cam shaft connected to the switching tappet; and in response to an engine braking condition associated with the internal combustion engine, locking an outer member of the switching tappet to the inner member to open the exhaust valve during a compression stroke of the cylinder with the outer member of the switching tappet acting on a second cam lobe of the cam shaft. 
     According to another aspect the method includes the internal combustion engine system includes an exhaust system for receiving exhaust gas produced by combustion of a fuel provided to at least a portion of the plurality of cylinders from a fueling system, and at least one turbine and at least one aftertreatment device in the exhaust system. 
     According to another aspect the method includes each of the plurality of cylinders is connected to a respective one of a plurality of switching tappets. 
     According to another aspect the method includes the outer tappet extends around and houses the inner tappet. 
     According to another aspect the method includes locking the outer member to the inner member includes hydraulically actuating a locking pin in one of the inner and outer members to extend between the inner and outer members. 
     According to another aspect the method includes in response to a compression release condition associated with the internal combustion engine, using a cam phaser to move the compression braking profile to provide a compression release condition. 
     According to another aspect the method includes a default position of the cam phaser is the compression release condition. 
     According to another aspect a system, comprising an internal combustion engine including a plurality of cylinders that receive a charge flow from an intake system for combustion of a fuel provided to at least a portion of the plurality of cylinders; at least one sensor operable to provide signals indicating operating conditions of the system; a valve actuation mechanism configured to control an opening and closing timing of exhaust valves associated with the plurality of cylinders, wherein the valve actuation mechanism includes a switching tappet associated with an exhaust valve of each of the plurality of cylinders, the switching tappet including an inner tappet in contact with a first cam lobe configured to open the exhaust valve during an exhaust stroke of the associated cylinder; and a controller connected to the at least one sensor operable to interpret one or more signals from the at least one sensor, wherein the controller, in response to an engine braking request based on the one or more signals, is configured to control the valve actuation mechanism to lock the inner member of the switching tappet with an outer member of the switching tappet, the outer member in contact with a second cam lobe configured to open the exhaust valve during a compression stroke of the associated cylinder. 
     According to another aspect the system includes the outer member extends around the inner member and the inner member is bucket shaped. 
     According to another aspect the system includes the switching tappet includes a locking pin housed in one of the inner and outer members so that the inner and outer members are movable relative to one another and the locking pin is hydraulically actuated to extend between and lock the inner and outer members to one another during engine braking. 
     According to another aspect the system includes the outer member includes a cylindrical body that houses the inner member therein. 
     According to another aspect the system includes the inner member moves independently of the outer member during the exhaust stroke of the cylinder. 
     According to another aspect the system includes a cam phaser operably connected to the internal combustion engine; wherein the controller, in response to a compression release condition based on the one or more signals, is configured to lock the cam phaser in a compression release condition. 
     According to yet another aspect a system comprising an internal combustion engine including a plurality of cylinders that receive a charge flow from an intake system for combustion of a fuel provided to at least a portion of the plurality of cylinders; at least one sensor operable to provide signals indicating operating conditions of the system; a roller finger follower configured to control an opening and closing timing of exhaust valves associated with the plurality of cylinders, the roller finger follower having an inner roller follower arm disposed adjacent an outer sliding follower; and a controller connected to the at least one sensor operable to interpret one or more signals from the at least one sensor, wherein the controller, in response to an engine braking request based on the one or more signals, is configured to control the roller finger follower to lock the inner roller follower arm of the roller finger follower with the outer sliding follower of the roller finger follower, the outer sliding follower in contact with a second cam lobe configured to open the exhaust valve during a compression stroke of the associated cylinder. 
     According to another aspect the system includes the inner roller follower arm is operatively connected to the outer sliding follower via a locking mechanism. 
     According to another aspect the system includes the internal combustion engine system includes an exhaust system for receiving exhaust gas produced by combustion of a fuel provided to at least a portion of the plurality of cylinders from a fueling system, and at least one turbine and at least one aftertreatment device in the exhaust system. 
     According to another aspect the system includes a cam phaser operably connected to the internal combustion engine; wherein the controller, in response to a compression release condition based on the one or more signals, is configured to lock the cam phaser in a compression release condition. 
     According to another aspect a method, comprises receiving a charge flow into a plurality of cylinders of an internal combustion engine system from an intake system, the internal combustion engine system including a valve actuation mechanism connected to each of the plurality of cylinders wherein the valve actuation mechanism includes an outer member lockable with an inner member to control an opening and closing timing of exhaust valves associated with the plurality of cylinders, receiving at least one signal from at least one sensor operably connected to a controller of the internal combustion engine system, the at least one signal indicating operating conditions of the system; operating the valve actuation mechanism having a compression release profile in response to a compression release condition associated with the internal combustion engine, the valve actuation mechanism locking the outer member to the inner member of the valve actuation mechanism to open the exhaust valve during a compression stroke of the cylinder with the outer member acting on a second cam lobe of the cam shaft and the inner member acting on a first cam lobe of the cam shaft; and locking a cam phaser operably connected to the internal combustion engine in a compression release condition. 
     According to another aspect the method includes operating the cam phaser in a default position that includes a compression release condition. 
     According to yet another aspect the method includes operating the valve actuation mechanism having a compression brake valve profile in response to a compression brake condition, the valve actuation mechanism locking the outer member to the inner member of the valve actuation mechanism to open the exhaust valve during a compression stroke of the cylinder with the outer member acting on a second cam lobe of the cam shaft and the inner member acting on a first cam lobe of the cam shaft. 
     According to yet another aspect the method includes in response to the compression brake condition, operating the cam phaser in an active position that includes a compression brake condition. 
     According to yet another aspect the method includes the valve actuation mechanism includes a roller finger follower. 
     According to yet another aspect the method includes the valve actuation mechanism includes a switching tappet. 
     According to yet another aspect the method includes the internal combustion engine system includes an exhaust system for receiving exhaust gas produced by combustion of a fuel provided to at least a portion of the plurality of cylinders from a fueling system, and at least one turbine and at least one aftertreatment device in the exhaust system. 
     According to yet another aspect the method includes locking the outer member to the inner member includes hydraulically actuating a locking pin in one of the inner and outer members to extend between the inner and outer members. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain exemplary embodiments have been shown and described. Those skilled in the art will appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. 
     In reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.