Abstract:
A switchable rocker arm for valve deactivation is provided for a valve train of an internal combustion engine. The switchable rocker arm includes a valve side lever assembly, a cam side lever assembly, and a hydraulically actuated coupling assembly. The valve side lever assembly includes a first housing with a first rocker shaft bore. The cam side lever assembly includes a second housing with a first arm with a second rocker shaft bore and a second arm with a third rocker shaft bore. The first and second arms extend along opposed longitudinal sides of the cam side lever assembly such that the first, second and third rocker shaft bores are axially aligned. The coupling assembly is arranged at an end furthest away from a pivot axis for minimal loading and provides locking and unlocking of the switchable rocker arm to achieve full valve lift and no valve lift modes, respectively.

Description:
BACKGROUND 
       [0001]    The present invention relates to a switchable rocker arm for a valve train of an internal combustion (IC) engine, and more particularly, to the coupling assembly of a switchable rocker arm that provides two discrete valve lift modes. 
         [0002]    More stringent fuel economy regulations in the transportation industry have prompted the need for improved efficiency of the IC engine. Lightweighting, friction reduction, thermal management, variable valve timing and a diverse array of variable valve lift technologies are all part of the technology toolbox for IC engine designers. 
         [0003]    Variable valve lift (VVL) systems typically employ a technology in a valve train of an IC engine that allows different engine valve lifts to occur. The valve train consists of the components that are required to actuate an engine valve, including a camshaft (also termed “cam”), the valve, and all components that lie in between. VVL systems are typically divided into two categories: continuous variable and discrete variable. Continuous variable valve lift systems are capable of varying a valve lift from a design lift minimum to a design lift maximum to achieve any of several lift heights. Discrete variable valve lift systems are capable of switching between two or three distinct valve lifts. Components that enable these different valve lift modes are often called switchable valve train components. Typical two-step discrete valve lift systems switch between a full valve lift mode and a partial valve lift mode, often termed cam profile switching, or between a full valve lift mode and a no valve lift mode that facilitates deactivation of the valve. Valve deactivation can be applied in different ways. In the case of a four-valve-per-cylinder configuration (two intake+two exhaust), one of two intake valves can be deactivated. Deactivating only one of the two intake valves can provide for an increased swirl condition that enhances combustion of the air-fuel mixture. In another scenario, all of the intake and exhaust valves are deactivated for a selected cylinder which facilitates cylinder deactivation. On most engines, cylinder deactivation is applied to a fixed set of cylinders, when lightly loaded at steady-state speeds, to achieve the fuel economy of a smaller displacement engine. A lightly loaded engine running with a reduced amount of active cylinders requires a higher intake manifold pressure, and, thus, greater throttle plate opening, than an engine running with all of its cylinders in the active state. Given the lower intake restriction, throttling losses are reduced in the cylinder deactivation mode and the engine runs with greater efficiency. For those engines that deactivate half of the cylinders, it is typical in the engine industry to deactivate every other cylinder in the firing order to ensure smoothness of engine operation while in this mode. Deactivation also includes shutting off the fuel to the dormant cylinders. Reactivation of dormant cylinders occurs when the driver demands more power for acceleration. The smooth transition between normal and partial engine operation is achieved by controlling ignition timing, cam timing and throttle position, as managed by the engine control unit (ECU). Examples of switchable valve train components that serve as cylinder deactivation facilitators include roller lifters, pivot elements, rocker arms and camshafts; each of these components is able to switch from a full valve lift mode to a no valve lift mode. The switching of lifts occurs on the base circle or non-lift portion of the camshaft; therefore the time to switch from one mode to another is limited by the time that the camshaft is rotating through its base circle portion; more time for switching is available at lower engine speeds and less time is available at higher engine speeds. Maximum switching engine speeds are defined by whether there is enough time available on the base circle portion to fully actuate a coupling assembly to achieve the desired lift mode. 
         [0004]    The precision of control of the deactivated cylinders varies within the engine industry. For optimum performance of the system, selective cylinder control rather than simultaneous multiple cylinder control is recommended. With selective cylinder control, the timing of the valve deactivation event with respect to the combustion cycle is maintained for each individual cylinder; for example, in a selective cylinder control system, an exhaust charge is normally trapped in the cylinder, which serves as an air spring and aids oil control during the deactivated mode. This is typically accomplished by deactivating the exhaust valve(s) first, followed by deactivation of the intake valve(s) of a given cylinder. With simultaneous multiple cylinder control, the timing of the valve deactivation event with respect to the combustion cycle is not controlled to the extent of the selective cylinder control resulting in intermittent exhaust charge trapping. 
         [0005]    In today&#39;s IC engines, many of the switchable valve train components that enable valve deactivation for cylinder deactivation contain a coupling or locking assembly that is actuated by an electro-hydraulic system. The electro-hydraulic system typically contains at least one solenoid valve within an array of oil galleries that manages engine oil pressure to either lock or unlock the coupling assembly within the switchable valve train component to enable a valve lift switching event. These types of electro-hydraulic systems require time within the combustion cycle to actuate the switchable valve train component. 
         [0006]    In most IC engine applications, switchable valve train components for cylinder deactivation in an electro-hydraulic system are classified as “pressureless-locked”, which equates to: 
         [0007]    a). In a no or low oil pressure condition, the spring-biased coupling assembly will be in a locked position, facilitating the function of a standard valve train component that translates rotary camshaft motion to linear valve motion; and, 
         [0008]    b). In a condition in which engine oil pressure is delivered to the coupling assembly that exceeds the force of the coupling assembly bias spring, the coupling assembly will be displaced a given stroke to an unlocked position, facilitating valve deactivation where the rotary camshaft motion is not translated to the valve. 
         [0009]    “Pressureless-unlocked” electro-hydraulic systems can be found in some cam profile switching systems that switch between a full valve lift and a partial valve lift, which equates to: 
         [0010]    a). In a no or low oil pressure condition, the spring-biased coupling assembly will be in an unlocked position, facilitating a partial valve lift event; and, 
         [0011]    b). In a condition in which engine oil pressure is delivered to the coupling assembly that exceeds the force of the coupling assembly bias spring, the coupling assembly will be displaced a given stroke to a locked position, facilitating a full valve lift event. 
         [0012]    With the successful implementation of cylinder deactivation systems on millions of production engines, engine manufacturers are now looking to expand the operating range. Examples include switching at higher engine speeds along with switching at colder oil temperatures. In addition, a new type of cylinder deactivation is in development that expands the deactivated mode operating range, increases the number of deactivating cylinders, and increases the frequency of switching in and out of a deactivated mode. In this new type of cylinder deactivation, all cylinders, as opposed to a group of cylinders, are continuously switched on and off depending on the demanded engine output. By controlling the engine output over a larger operating range in this way instead of by conventional throttling, pumping losses are reduced even further compared to traditional cylinder deactivation systems and, thus, a higher engine efficiency is achieved. 
         [0013]    Vital to the durability and performance of a switchable valve train component is the robustness of the coupling assembly. Two important design attributes of the coupling assembly include: 1). the ability to switch from a locked to an unlocked position very quickly, and 2). a high resistance to wear. However, many times these attributes are in opposition. For example, the locking/unlocking stroke of the coupling assembly to engage/disengage an adjacent component has a direct impact on switching times; a shorter stroke for a given cross-sectional area of a coupling assembly will likely yield a faster switching time. Yet, a shorter stroke typically dictates a smaller contact area with the engaged or disengaged component, meaning that a given load is applied over a smaller area leading to higher contact pressures and subsequent wear. For this reason, various coupling assembly forms, materials, coatings and heat treatments are often employed in an effort to maximize wear resistance in order to minimize the actuation stroke and resultant contact area. 
         [0014]    Given the aforementioned design challenges and more stringent switching time demands for switchable valve train components, a coupling assembly for improved wear and actuation times is required. Therefore, a primary objective of this invention is to locate the coupling assembly at a position within a switchable rocker arm that reduces the load and resultant wear on the coupling assembly. 
       SUMMARY 
       [0015]    A switchable rocker arm for valve deactivation that pivots about a rocker shaft is provided for a valve train of an internal combustion engine. The switchable rocker arm includes a valve side lever assembly, a cam side lever assembly, and a hydraulically actuated coupling assembly. The hydraulically actuated coupling assembly is located at a position within the switchable rocker arm that minimizes loads and resultant wear on the coupling assembly. The hydraulically actuated coupling assembly facilitates two valve lift modes: a full valve lift mode and a no valve lift mode. The full valve lift mode is achieved when the valve side lever assembly is coupled or locked to the cam side lever assembly; thereby, when a camshaft rotationally actuates the cam side lever assembly, both assemblies pivot together in unison about the rocker shaft, allowing rotary motion of the camshaft to be translated to linear motion of an engine valve. The no valve lift mode results when the valve side lever assembly is uncoupled or unlocked from the cam side lever assembly; thereby, when the camshaft rotationally actuates the cam side lever assembly, only the cam side lever assembly rotates about the rocker shaft while the valve side lever assembly remains stationary, preventing translation of the rotary motion of the camshaft to the engine valve. 
         [0016]    The valve side lever assembly includes a first housing with two axially offset arms at one end defining a cavity, and a valve interface and shuttle pin bore that houses a hydraulically actuated shuttle pin at an opposite end. The valve interface can be in the form of a hydraulic lash adjuster, as provided in a first embodiment, or an adjusting screw assembly, as provided in a second embodiment. Each of the two arms has a rocker shaft bore to interface with and pivot about the rocker shaft. 
         [0017]    The cam side lever assembly includes a second housing with a cam interface at one end, a locking pin bore at an opposite end, and a rocker shaft bore between the two ends to pivot about the rocker shaft. The cam side lever assembly resides in the cavity formed by the two offset arms of the first housing of the valve side lever assembly in such a way that the two rocker shaft bores of the first housing are axially aligned with the rocker shaft bore of the second housing. A limited rotational position of the cam side lever assembly with respect to the valve side lever assembly is provided by two inwardly protruding stops located on each of the two axially offset arms of the first housing of the valve side lever assembly. The cam interface can be in the form of a roller follower assembly or a sliding pad. The locking pin bore houses a locking pin, in contact with a bias spring or resilient element that is displaced by the adjacent hydraulically actuated shuttle pin. Optionally, a sleeve can be arranged within the locking pin bore to house the locking pin. 
         [0018]    The locking pin moves in a longitudinal direction within the locking pin bore (or sleeve) to achieve a first locked position and a second unlocked position. The first locked position results when the locking pin bore of the second housing is axially aligned with the shuttle pin bore of the first housing, enabling engagement of the locking pin with both the locking pin bore and the shuttle pin bore. In this position, the bias spring or resilient element in contact with one end of the locking pin is compressed and provides a pre-load to the locking pin; additionally, the position of the locking pin is defined by a first distance from an outer end of the locking pin to a blind or closed end of the locking pin bore, and the position of the shuttle pin is defined by a second distance from an outer end of the shuttle pin to a blind or closed end of the shuttle pin bore. The first locked position fulfills a full valve lift or activated valve mode during which rotational cam lift is translated to linear valve lift. 
         [0019]    The second unlocked position results when hydraulic pressure, typically engine oil pressure, is applied to the adjacent shuttle pin engaged with the locking pin. The force created by the hydraulic pressure acting on the shuttle pin overcomes the pre-load of the compressed bias spring acting on the adjacent locking pin, causing the locking pin to move longitudinally to the second unlocked position at which the locking pin is disengaged with the shuttle pin bore. In this unlocked position, the bias spring contacting the locking pin is compressed further than in the first locked position; additionally, compared to the first unlocked position, the locking pin is closer to the closed end of the locking pin bore, defined by a third distance, and the shuttle pin is further away from the closed end of the shuttle pin bore, defined by a fourth distance. While in the second unlocked mode, the cam side lever assembly is rotationally displaced about the rocker shaft by the camshaft separately from the valve side lever assembly, which remains stationary, fulfilling a no valve lift or deactivated valve mode. A lost motion spring or resilient element is arranged between the cam side and valve side arm assemblies to provide a force during the second unlocked mode that can, a). control the motion of the cam side lever assembly such that separation with the camshaft does not occur at a maximum deactivation engine speed, and, b). act upon the valve side lever assembly to prevent pump-up of the optional hydraulic lash adjuster. 
         [0020]    Multiple variations of an oil gallery or fluid passage network within the first housing of the valve side lever assembly are possible to transport oil from the rocker shaft to accommodate the previously described functions and component options. For a fluid passage network of the first embodiment of the switchable rocker arm that contains a hydraulic lash adjuster to serve as the valve interface, the shuttle pin can receive hydraulic fluid from at least one fluid passage within either or both axially offset arms that first feeds the hydraulic lash adjuster, followed by the shuttle pin, in series. In a variation of this fluid passage, separate fluid passages for the shuttle pin and hydraulic lash adjuster can exist within either or both arms for the hydraulic lash adjuster and shuttle pin. A fluid passage network for the second embodiment of the switchable rocker arm that contains an adjusting screw assembly to serve as the valve interface requires only a fluid passage or passages within either or both of the axially offset arms to feed the shuttle pin. The adjusting screw assembly typically does not need an oil feed, however, if one is needed, either of the previously described fluid passage networks could be applied. 
         [0021]    A location of the hydraulically actuated coupling assembly within the switchable rocker arm is specified at the valve end of the switchable rocker arm in order to facilitate a maximum distance between a locking interface and the switchable rocker arm pivot point. While in the first locked position that facilitates the full valve lift mode, the switchable rocker arm is subjected to a load throughout the valve lift event causing the locking pin to be loaded in shear due to its partial position within the locking pin bore and the shuttle pin bore. A magnitude of this shear load is proportional to a distance from the rocker arm pivot point to where the locking pin is loaded in shear. Therefore, placement of the coupling assembly at a location that is furthest away from the rocker arm pivot point will yield lower shear loads and subsequently lower wear of the coupling assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The foregoing Summary as well as the following Detailed Description will be best understood when read in conjunction with the appended drawings. In the drawings: 
           [0023]      FIG. 1  is a perspective view of a first embodiment of a switchable rocker arm. 
           [0024]      FIG. 2  is perspective view of a valve side lever assembly of the switchable rocker arm of  FIG. 1 . 
           [0025]      FIG. 3  is a perspective view of a cam side lever assembly of the switchable rocker arm of  FIG. 1 . 
           [0026]      FIG. 4  is a cross-sectional view of the switchable rocker arm of  FIG. 1  in a first locked position. 
           [0027]      FIG. 5  is a cross-sectional view of the switchable rocker arm of  FIG. 1  in a second unlocked position. 
           [0028]      FIG. 6  is a top view of a schematic of a fluid passage network for the switchable rocker arm of  FIG. 1 . 
           [0029]      FIG. 7  is a top view of a variation of a schematic of a fluid passage network for the switchable rocker arm of  FIG. 1 . 
           [0030]      FIG. 8  is a top view of a schematic of a fluid passage network for a second embodiment of a switchable rocker arm. 
           [0031]      FIG. 9  is a perspective view of the second embodiment of a switchable rocker arm. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Certain terminology is used in the following description for convenience only and is not limiting. The words “inner,” “outer,” “inwardly,” and “outwardly” refer to directions towards and away from the parts referenced in the drawings. A reference to a list of items that are cited as “at least one of a, b, or c” (where a, b, and c represent the items being listed) means any single one of the items a, b, c or combinations thereof. The terminology includes the words specifically noted above, derivatives thereof, and words of similar import. 
         [0033]    Referring to  FIGS. 1 through 5 , a first embodiment of a switchable rocker arm  10  that provides for reduced coupling assembly loads is shown. The switchable rocker arm  10  is capable of switching between two discrete valve lift modes. The components of the switchable rocker arm  10  include a valve side lever assembly  12 , a cam side lever assembly  14 , a first lost motion spring  16 A, and a second lost motion spring  16 B. Those familiar with switchable valve train components are aware that various forms of lost motion springs are possible. The switchable rocker arm  10  rotates about a pivot axis  11  of a rocker shaft (not shown), which is typical for shaft-mounted switchable rocker arms. 
         [0034]    Referring to  FIG. 2 , the valve side lever assembly  12  for the first embodiment of a switchable rocker arm  10  is shown. The valve side lever assembly  12  includes a first housing  22  having a first end with a first arm  24 A and a second arm  24 B, such that the first arm  24 A is axially offset from the second arm  24 B, creating a space or passage  25  in between the two arms  24 A, 24 B. The first arm  24 A includes a first rocker shaft bore  26 A and the second arm  24 B includes a second rocker shaft bore  26 B. A first stop  28 A protrudes inwardly from a first inner wall  27 A on the first arm  24 A and a second stop  28 B protrudes inwardly from a second inner wall  27 B on the second arm  24 B; the first and second stops  28 A, 28 B limit the rotation of the cam side lever assembly  14  with respect to the valve side lever assembly  12 . A first retainer post  30 A for the first lost motion spring  16 A is present on a first outer wall  29 A of the first arm  24 A. A second retainer post  30 B for the second lost motion spring  16 B is present on a second outer wall  29 B of the second arm  24 B. A second end of the first housing  22  has a valve interface in the form of a hydraulic lash adjuster  20  and a shuttle pin bore  37 . A second fluid passage  44  extends from the second rocker shaft bore  26 B to the hydraulic lash adjuster  20 ; a third fluid passage  46 , visible in  FIGS. 4 and 5 , extends from the hydraulic lash adjuster  20  to a second closed end of the shuttle pin bore  37 . 
         [0035]    Referring specifically to  FIG. 3 , the cam side lever assembly  14  for the first embodiment of a switchable rocker arm  10  is shown. The cam side lever assembly  14  includes a second housing  32  having a third end with a cam interface in the form of a roller follower  18 , and a fourth end with a locking pin bore  35  that houses an optional sleeve  38  for guiding and interfacing with a locking pin  34 . Without the presence of the optional sleeve  38 , the locking pin  34  would interface directly with the locking pin bore  35 . Other forms of cam interfaces at the third end of the second housing  32  are possible such as a slider pad. A third retainer post  31 A for the first lost motion spring  16 A is present on a third outer side  33 A of the third end of the second housing  32 . A fourth retainer post  31 B for the second lost motion spring  16 B is present on a fourth outer side  33 B of the third end of the second housing  32 . A third rocker shaft bore  26 C is present at a medial position on the second housing  32 . The cam side lever assembly  14  fits within the space or passage  25  created by the two arms  24 A, 24 B of the first housing  22  of the valve side lever assembly  12 , such that the first arm  24 A extends along a first longitudinal side  48 A of the second housing  32 , and the second arm  24 B extends along a second longitudinal side  48 B of the second housing  32 . In addition, the third rocker shaft bore  26 C is in axial alignment with the first and second rocker shaft bores  26 A, 26 B of the first and second arms  24 A, 24 B, respectively, of the first housing  22 . 
         [0036]    The switchable rocker arm  10  captured in  FIGS. 1 through 5  is capable of switching between two discrete valve lift modes, achieved by different longitudinal positions of the locking pin  34 . Referring now to  FIG. 4 , a first locked position is shown at which the locking pin bore  35  of the second housing  32  is axially aligned with the shuttle pin bore  37  of the first housing  22 , enabling engagement of the locking pin  34  with both the first housing  22  and the second housing  32 . More specifically, the locking pin  34  is engaged with both the shuttle pin bore  37  of the first housing  22  and the optional sleeve  38  arranged within the locking pin bore  35  of the second housing  32 . If the optional sleeve  38  is not present, the locking pin  34  would engage directly with the locking pin bore  35 . The first locked position facilitates a full valve lift mode such that when the cam side lever assembly  14  is rotationally actuated by the cam, the valve side lever assembly  12  rotates in unison with the cam side lever assembly  14  about the pivot axis  11 . In the first locked position, a locking pin bias spring or resilient element  40  with a first compressed length C 1 , urges the locking pin  34  with a pre-load force to its shown position in  FIG. 4 . The shown position of the locking pin  34  can be defined or limited by either of two design features: 1). (as shown) the adjacent shuttle pin  36  with a first end engaging the locking pin  34 , reaches a second closed or blind end of the shuttle pin bore  37 , or 2). any other suitable means of limiting the longitudinal travel of the locking pin  34  within the shuttle pin bore  37 . At the first locked position, a third outer end of the locking pin  34  is at a first distance L 1  from a fourth closed or blind end of the locking pin bore  35 , while the first end of the shuttle pin  36  is at a second distance L 2  from a second closed or blind end of the shuttle pin bore  37 . 
         [0037]    Referring now to  FIG. 5 , a second unlocked position is shown in which the locking pin  34  is completely retracted from the shuttle pin bore  37 . This occurs when hydraulic fluid, typically at an engine fluid pump pressure, is delivered to the second closed end of the shuttle pin bore  37  and acts upon the second end of the shuttle pin  36 . The force created by the hydraulic pressure acting on the shuttle pin  36  overcomes the pre-load urging force of the compressed bias spring  40  acting on the adjacent and engaged locking pin  34 , causing the locking pin  34  to move longitudinally until it disengages the shuttle pin bore  37 . Therefore, the third or outer end of the locking pin  34  is closer to the fourth or closed end of the locking pin bore  35 , defining a third distance L 3 , and the first end of the shuttle pin  36  is further away from the second or closed end of the shuttle pin bore  37 , defining a fourth distance L 4 . In the second unlocked position, the bias spring  40  compresses to a second compressed length C 2  that is shorter than the first compressed length C 1  in the first locked position. The second unlocked position facilitates a no valve lift mode in which the cam side lever assembly  14  is rotationally displaced about the pivot axis  11  by the camshaft independently from the valve side lever assembly  12 , which remains stationary. While in the no valve lift or deactivation mode, the first and second lost motion springs  16 A, 16 B provide a force that can: 1). act upon the cam side lever assembly via the third and fourth retainer posts  31 A, 31 B, controlling the motion of the cam side lever assembly  14  such that separation with the camshaft does not occur at a maximum deactivation speed, and 2). act upon the valve side lever assembly  12  via the first and second retainer posts  30 A, 30 B to prevent a pump-up or extended length condition of the hydraulic lash adjuster  20  which could hinder the switching function of the switchable rocker arm  10 . 
         [0038]    Referring again to  FIG. 4 , an alternative locking pin  34 A and an alternative sleeve  38 A are shown with broken lines. Compared to the previously described locking pin  34  and sleeve  38 , the location of the alternative locking pin and sleeve  34 A, 38 A are instinctive due to their proximity to the pivot axis  11 , requiring low effort to integrate a short and simple hydraulic gallery for actuation of the locking pin  34 A. However, analyzing the moment about the pivot axis  11  created by the reactive forces that correspond to each of the two locking pin positions provides further insight into the ideal location for a locking pin. A force F V  applied to the hydraulic lash adjuster  20  (or other suitable valve interface) of the switchable rocker arm  10  by an engine valve (not shown) creates a moment about the pivot axis  11  equal to the magnitude of the force F V  multiplied by a magnitude of a vector d V , as shown in  FIG. 4  and by the equation below: 
         [0000]    
       
      
       M 
       11 
       =F 
       v 
       ×d 
       v  
      
       
         
           
             where: d V =perpendicular distance from the pivot axis  11  to a line of action of the force F V . 
           
         
       
     
         [0040]    To counteract this moment created on the switchable rocker arm  10  by the engine valve, a counter-moment is present about the central axis  11  created by a reactive force F 34  of the locking pin  34 , hereafter termed “reactive shear force”, multiplied by a magnitude of vector d 34 . Assuming that a sum of moments about the pivot axis  11  is zero, the reactive shear force F 34  can be expressed as shown below: 
         [0000]    
       
         
           
             
               + 
               
                 ∑ 
                 
                     
                 
                  
                 
                   M 
                   11 
                 
               
             
             = 
             0 
           
         
       
       
         
           
             
               
                 ( 
                 
                   
                     F 
                     34 
                   
                   × 
                   
                     d 
                     34 
                   
                 
                 ) 
               
               - 
               
                 ( 
                 
                   
                     F 
                     v 
                   
                   × 
                   
                     d 
                     v 
                   
                 
                 ) 
               
             
             = 
             0 
           
         
       
       
         
           
             
               F 
               34 
             
             = 
             
               
                 ( 
                 
                   
                     F 
                     v 
                   
                    
                   
                     d 
                     v 
                   
                 
                 ) 
               
               
                 d 
                 34 
               
             
           
         
       
       
         
           
             where: d 34 =perpendicular distance from the pivot axis  11  to a line of action of the reactive shear force F 34 . 
           
         
       
     
         [0042]    One can observe that the magnitude of the reactive shear force F 34  of the locking pin  34  is inversely proportional to the magnitude of vector d 34 . Therefore, as the magnitude of vector d 34  increases, the reactive shear force F 34  applied to the locking pin  34  decreases. Furthermore, with reference to  FIG. 4  and the distance vectors d 34  and d 34A  for the respective locations of the locking pin  34  located at the fourth end of the second housing  32  and the alternative locking pin  34 A, the following equation provides an amount of reactive shear force reduction due to a more distant locking pin: 
         [0000]    
       
         
           
             
               reactive 
                
               
                   
               
                
               shear 
                
               
                   
               
                
               force 
                
               
                   
               
                
               reduction 
                
               
                   
               
                
               
                 ( 
                 % 
                 ) 
               
             
             = 
             
               
                 
                   ( 
                   
                     
                       d 
                       34 
                     
                     - 
                     
                       d 
                       
                         34 
                          
                         
                             
                         
                          
                         A 
                       
                     
                   
                   ) 
                 
                 
                   d 
                   34 
                 
               
               × 
               100 
             
           
         
       
       
         
           
             where: d 34 =perpendicular distance from the pivot axis  11  to a line of action of the reactive shear force F 34 . 
             d 34A =perpendicular distance from the pivot axis  11  to a line of action of the reactive shear force F 34A . 
           
         
       
     
         [0045]    Quantifying the difference in reactive shear force between the two locking pin locations, a distance of 14 millimeters is assumed for d 34A  that corresponds with the alternative locking pin  34 A shown in broken lines, and a distance of 28 millimeters is assumed for d 34  that corresponds with the locking pin  34  shown in solid lines. Using the equation for reactive shear force reduction, a reduction of 50% is achieved by locating the locking pin  34  at the fourth end of the second housing  32  versus the less distant location of the alternative locking pin  34 A, providing significantly reduced locking pin stress and resulting wear. 
         [0046]    Referring to  FIG. 9 , a second embodiment of a switchable rocker arm  80  is shown that utilizes an adjusting screw assembly  70  as a valve interface which potentially reduces the complexity and cost of the switchable rocker arm  80 . 
         [0047]      FIGS. 6 through 8  show various oil gallery or fluid passage networks in schematic form to accommodate the first and second embodiments of switchable rocker arms  10 , 80 .  FIG. 6  shows a schematic of a fluid passage network for the first embodiment of a switchable rocker arm  10  that utilizes a hydraulic lash adjuster  20  at the second end of the first housing  22  of the valve side lever assembly  12 . Referencing  FIG. 6  together with the perspective view of the valve lever side assembly  12  of  FIG. 2 , a second fluid passage  44  is shown that extends from the second rocker shaft bore  26 B to the hydraulic lash adjuster  20 . Optionally, an additional second fluid passage  45  can be utilized that extends from the first rocker shaft bore  26 A to the hydraulic lash adjuster  20 . A third fluid passage  46  extends from the hydraulic lash adjuster  20  to the second closed end of the shuttle pin bore  37 . Thus, for the fluid passage network shown in  FIG. 6 , hydraulic fluid is provided first to the hydraulic lash adjuster  20 , and then second to the second end of the shuttle pin  37 , in series. 
         [0048]      FIG. 7  shows a variation of a fluid passage network for the first embodiment of a switchable rocker arm  10  that utilizes a hydraulic lash adjuster  20  at the second end of the first housing  22  of the valve side lever assembly  12 . Referring to  FIG. 7  together with the perspective view of the valve lever side assembly  12  in  FIG. 2 , separate fluid passages exist for the hydraulic lash adjuster  20  and the shuttle pin bore  37 . The second fluid passage  44  and optional additional second fluid passage  45  from  FIG. 6  remain in  FIG. 7 &#39;s network; however, in this variation, the shuttle pin bore  37  receives hydraulic fluid via a first fluid passage  42  that extends from the second rocker shaft bore  26 B to the second end of the shuttle pin bore  37 . Optionally, an additional first fluid passage  43  can be utilized that extends from the first rocker shaft bore  26 A to the second closed end of the shuttle pin bore  37 . 
         [0049]      FIG. 8  shows a fluid passage network for the second embodiment of a switchable rocker arm  80  that utilizes an adjusting screw assembly  70  as a valve interface. Since the adjusting screw assembly  70  does not typically require a hydraulic fluid feed,  FIG. 8 &#39;s fluid passage network is the simplest of the three fluid passage networks shown, requiring only the first fluid passage  42  and the optional additional first fluid passage  43  that extend from the second and first rocker shaft bores  26 B, 26 A to the second end of the shuttle pin bore  37 . In the event that the design of the adjusting screw assembly  70  incorporates a means of lubricating the interface with the valve and, thus, requires an oil feed, the fluid passage networks of either  FIG. 6  or  FIG. 7  could be applied. 
         [0050]    Having thus described various embodiments of the present switchable rocker arm in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description above, could be made in the apparatus without altering the inventive concepts and principles embodied therein. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.