Abstract:
A roller finger follower is provided having a housing and two separate outer arms mounted at one end to a pivot axle that extends through the housing. A roller is mounted in the housing The outer arms extend longitudinally along sides of the housing and include high lift cam contact surfaces. The outer arms having an outer arm body and separately formed longitudinal body, retained on the outer arm body, the longitudinal body including the cam contact surface. The longitudinal body is formed of a high durability material or coated with a suitable coating, the outer arm body formed of a lower grade, lower cost material.

Description:
TECHNICAL FIELD 
       [0001]    Example aspects described herein relate to roller finger followers that are used in overhead cam type internal combustion engines and, more particularly, to switchable roller finger followers. 
       BACKGROUND 
       [0002]    Switchable roller finger followers are known. See, for example, U.S. Pat. No. 7,174,869. Such finger followers have an outer lever pivotably mounted outside an inner lever and a roller rotatably mounted on a transverse axle in a slot in the inner lever. The top surface of the outer lever acts as a contact surface for a high lift cam and the top surface of the roller acts as a contact surface for a low lift cam. A coupling element is mounted at one end of the finger and oil from an oil source is used to activate the coupling element. When the coupling element is activated, it locks the outer lever to the inner lever and requires the follower to follow the high lift cam and transfer the lift to the valve stem of an associated intake or exhaust valve. When the coupling element is deactivated, the outer lever is free to pivot relative to the inner lever and, under the aid of a spring, the outer lever pivots freely in conjunction with the high lift cam while the motion of the low lift cam is transferred by the inner lever to the valve stem. This movement by the outer lever is conventionally referred to as the lost motion stroke. 
         [0003]    Conventionally, the outer lever is a unitary structure such that the coupling element need only operate on one part of the outer lever. Typically, the coupling device operates on a yoke portion of the outer lever, the yoke portion being transverse to the longitudinal axis of the finger follower. Conventionally, the roller axle is staked to the inner lever to maintain its lateral position relative to the inner lever. U.S. Pat. No. 7,909,007 discloses a roller finger follower of this type. This provides a lost motion spring to maintain contact between the cam follower and the cam. 
         [0004]    US2011/0197843 discloses the inventor&#39;s prior switchable roller finger follower in which the outer arm is formed by two separate outer arms that can move independently from one another and are connected to a common coupling element. However, the outer arms have a fairly complex configuration and associated cost. In order to produce the separate arms, and associated sliding pad contacts, to withstand valvetrain, and more specifically, cam lobe loads, particular materials, such as bearing grade steel, or specific materials along with special coatings, such as diamond-like carbon coatings, are used. US2011/0197843 is incorporated herein by reference as if fully set forth. 
       SUMMARY 
       [0005]    Briefly stated, a roller finger follower is provided having a housing and two separate outer arms mounted at one end to a pivot axle that extends through an opening in a first end of the housing. A roller is rotatably mounted on a transverse axle in a slot in the housing. The outer arms extend longitudinally along sides of the housing towards the other end of the inner lever and include high lift cam contact surfaces located adjacent to the roller. Each of the outer arms are formed of at least two pieces; an outer arm body with a longitudinal depression at an upper periphery; and a longitudinal body of a size and shape to fit into the depression, and retained to the outer arm body by any known means, such as laser welding or press fitting. The outer arm body can be provided with a slot adjacent the depression to mate with a radially extending retention feature, extending from a lower periphery of the longitudinal body. The longitudinal body can be formed of high durability material, such as bearing steel or coated with a suitable coating, such as amorphous hydrocarbon. The outer arm body can be formed of a lower grade and lower cost material, such as tool steel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The foregoing Summary and the following detailed description will be better understood when read in conjunction with the appended drawings, which illustrate a preferred embodiment of the invention. In the drawings: 
           [0007]      FIG. 1  is a perspective view of a switchable finger follower according to one example embodiment; 
           [0008]      FIG. 2  is a side view of an outer arm for a switchable roller finger follower, with slider pad insert, according to one example embodiment; 
           [0009]      FIG. 3  is a perspective view of the outer arm with slider pad insert of  FIG. 2 ; 
           [0010]      FIG. 4  is a perspective view of the slider pad insert of  FIG. 2 ; 
           [0011]      FIG. 5  is a perspective view of the outer arm, without the slider pad insert, of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Certain terminology is used in the following description for convenience only and is not limiting. The words “front,” “rear,” “upper” and “lower” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer to directions toward 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, or c, or combinations thereof. The terminology includes the words specifically noted above, derivatives thereof and words of similar import. 
         [0013]      FIG. 1  shows a switchable finger follower  100  according to one example embodiment. Finger Follower  100  comprises main housing or primary lever  101 , low lift cam follower  102 , secondary lever or outer arms  1 , assembled onto pivot axle  112  and retained onto axle  112  by retention clips  113 , locking pin  103 , and lost motion springs  114 ,  115  assembled onto spring pin  116 . Secondary lever or outer arms  1  are selectively lockable and unlockable by longitudinal movement of locking pin  103 , orthogonal to pivot axis T of outer arms  1  and actuated by introduction of pressurized hydraulic fluid or any other known means. In another embodiment, a single secondary lever can replace outer arms  1  without impacting the scope of the present disclosure. High lift cam lobes (not shown) of a camshaft (not shown) contact upper contact surfaces  120  of arms  1 . Housing  101  includes wall  130 , wall  131  and interior space  132  at least partially formed by walls  130  and  131 . Low lift cam follower or roller  102  is inserted into space  132 , and retained in position by a transverse axle (not shown) extending substantially through walls  130 ,  131  and cam follower  102 . 
         [0014]    When locking pin  103  is in locked mode, namely, moved longitudinally inward, toward arms  1  and contacts lower contact arm  122 ,  123  of outer arms  1  the contact of high lift cam lobes with the respective upper contact surfaces  120  pivots finger follower  100  about an associated pivot element (not shown) at end B, and causes a high lift of an associated valve (not shown) at end A. When locking pin  103  is in unlocked mode, namely when moved longitudinally outward, away from arms  1 , the contact of high lift came lobes with upper contact surfaces  120  causes lost motion movement of outer arms  1  against spring arms  117 ,  118  of springs  115 ,  114 , respectively, in contact with outer arms  1  at lost motion guides  125 ,  126 , respectively. 
         [0015]      FIG. 2  is a side view of outer arm  1  for a switchable roller finger follower, including slider pad insert  2  and outer arm body  3 , according to one example embodiment.  FIG. 3  is a perspective view of outer arm  1  of  FIG. 2 .  FIGS. 4 and 5  are perspective views of slider pad insert  2  and outer arm body  3  of  FIG. 2 , respectively. The following description should be viewed in light of  FIGS. 2 through 5 . Outer arm  1  comprises two assembled pieces; slider pad insert  2 , made of a hard material, or a material suitable for coating, then coated, in order to withstand contact stresses associated with contact with cam lobes during operation; and outer arm body  3 , made of standard tool steel or other suitable material. In this embodiment, arm  1  would be one of two arms, such as that shown in follower  100 . It will be understood by one skilled in the art, that, although separate outer arms are described herein, slider pad inserts may be used in finger follower arrangements similar to that described in U.S. Pat. Nos. 7,174,869 and 7,909,007. 
         [0016]    In this example embodiment, slider pad insert  2  is comprised of an upper curved longitudinal piece  5 , with an upper contact surface  6  of a length and area required to accept contact with an associated cam lobe (not shown) for any particular application, such that the cam lobe does not have substantial contact with the upper surface of outer arm body  3  during operation, a lower retention piece  7  and a neck portion or post  8 , radially connecting longitudinal piece  5  with retention piece  7 . Retention piece  7  is shown as a rectangular parallelepiped, substantially shorter in length than longitudinal piece  5  and longer than neck portion or post  8 . In an example embodiment, retention piece  7  is ⅓ the length of longitudinal piece  5 , though one skilled in the art will understand that retention piece  7  can be longer. When slider pad insert  2  is inserted into outer arm body  3 , more specifically into insert slot  10 , lower radial surface  20  of radial retention tab  11  contacts upper radial surface  13  of retention piece  7 , and against side surface  14  of neck  8 , and lower surface  21  of tab  12  contacts upper radial contact surface  15  of retention piece  7  and side surface  16  of neck  8 . In this manner slider pad insert  2  is retained in a radial direction and in a direction orthogonal to pivot axis P of arm  1 . Slider insert pad  2  can be retained in a direction parallel to pivot axis P, by at least one of press fitting, staking, laser welding or any other suitable fixation means known in the art. It will be understood by one skilled in the art that retention of insert  2  within body  3  does not have to take the particular form described, but can take any variety of suitable forms, including, but, not limited to a triangular retention piece  7 , multiple retention pieces, retention pieces at longitudinal ends of upper longitudinal piece  5 , or, no retention piece, instead only using one of the means described, namely, staking, laser welding and the like. 
         [0017]    Outer arm body  3  can take a variety of forms, however, in the embodiment described, in addition to insert slot  10 , body  3  comprises pivot hole  31 , to receive pivot pin (not shown) of an associated finger follower assembly, lost motion spring arm guide  32  and depression  30 , of a length and depth such that upper contact  6  of insert  2  is coincident with upper radial periphery or surface  35  at both longitudinal ends of body  3 . 
         [0018]    As previously described, insert  2  is preferably made of a material suitable to withstand required contact pressures, such as one of bearing grade steel, for example SAE 52100, or a material suitable to accept a coating, for example X210CrW12 steel, coated on an outer surface with a suitable coating, such as an amorphous hydrocarbon. The amorphous hydrocarbon includes metal free amorphous hydrocarbon. The amorphous hydrocarbon also includes metal-free amorphous hydrocarbon with sp 2  and sp 3  hybridized carbon. Further detail regarding a layer of amorphous hydrocarbon, metal-free amorphous hydrocarbon, or metal-free amorphous hydrocarbon with sp 2  and sp a  hybridized carbon is provided in commonly-owned U.S. Pat. Nos. 7,363,894 and 8,161,925, which patents are incorporated in their entirety herein. Arm body  3  can be made of any suitable material, preferably low cost material, for example standard tool steel. 
         [0019]    While the preferred embodiment of the invention has been described in detail, those skilled in the art will recognize that other changes could be made to a switchable roller finger follower without departing from the scope of the present invention. Other types of arm or slider pad arrangements could be provided and the specific configuration of the insert relative to the roller finger follower and arm or wall could be varied without departing from the scope of the present invention. Accordingly, the scope of the invention should not be limited by the preferred embodiments discussed above and instead should be defined by the claims as noted below.