Patent Publication Number: US-7909007-B2

Title: Roller finger follower for valve deactivation

Description:
FIELD OF INVENTION 
     The invention relates to roller finger followers that are used in overhead cam type internal combustion engines and, more particularly, to switchable roller finger followers that have a high lift, low lift, and no lift mode. 
     BACKGROUND OF THE INVENTION 
     Switchable roller finger followers that have a high lift mode, a low lift mode, and a no lift mode are known. Typically, such finger followers have an outer elongated body, one end of which mates with a valve stem and operates on the valve stem, and a second end which is in contact with a hydraulic lash adjuster. An inner elongated body is centrally located in the outer elongated body and houses a cam follower that is operated on by the cam so as to provide motion to the finger follower. The inner elongated body has two modes, a locked mode and an unlocked mode. A latching mechanism is part of the finger follower and is used to lock the inner elongated body in a stationary position. When the inner elongated body is locked in a stationary position, the cam which is fixed to the cam shaft of the engine forces the movement of the finger follower which translates into the movement of the valve through the valve stem. In order to deactivate the finger follower, the latch is released and the inner elongated body is unlocked and can travel freely up and down in conjunction with the cam without transferring the motion of the cam to the finger follower. 
     In order to maintain contact between the cam and the cam follower during the unlocked periods, a lost motion spring is employed. A typical lost motion spring is either helical or torsional. 
     OBJECT OF THE INVENTION 
     It is the object of the invention to design a switchable roller finger follower for an overhead cam internal combustion engine having a low mass moment of inertia about the pivot axis of the finger follower. These and other objects of the present invention may be more fully understood by reference to the following description. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is achieved by locating the lost motion torsional spring device at the lash adjuster end of the finger follower, above the lash adjuster. 
     The lost motion torsional spring device has two helical spring parts which are coaxial with each other and mounted on the finger follower transverse to the long axis of the finger follower. Each of the helical parts has a long leg and a short leg. 
     In order to locate the lost motion torsional spring device above the lash adjuster at the lash adjuster end of the finger follower, lost motion spring pins and a lost motion spring stop are provided to the outer housing of the finger follower to secure the lost motion torsional spring device on the finger follower and lost motion spring pallets are located on the inner housing in which the cam follower is housed. The lost motion torsional spring device is mounted on the outer housing by positioning one of each of the helical parts on one of each of the pins. The pallets provide a contact surface for the long legs while the stop provides a contact surface for the short legs. The short legs can be joined such that the lost motion torsional spring device is a single spring or the short legs can be separate such that the two helical parts form two separate springs. 
     Broadly, the switchable roller finger follower of the present invention can be defined as follows:
         an outer elongated body having a valve stem end, a lash adjuster end, and two outer elongated body side walls;   a first inner cavity in said outer elongated body;   two lost motion spring pins attached to said lash adjuster end of said outer elongated body, said pins oriented transversely to a long axis of the outer elongated body;   a lost motion spring stop located on an outer wall of the elongated body and adjacent to said lash adjuster end;   an inner elongated body positioned in said first inner cavity and having a first end pivotally attached to said outer elongated body at said valve stem end, a second end adjacent to said lash adjuster end, and two inner elongated body side walls;   a second inner cavity in said inner elongated body;   two lost motion spring pallets, one of each of said pallets fixed on one of each of said inner elongated body side walls at said second end;   a center cam follower in said second inner cavity;   a latch assembly fixed to said outer elongated body at said lash adjuster end for preventing pivoting of the inner elongated body; and   a lost motion torsional spring device having two helical parts, one of each of said helical parts on one of each of said lost motion pins, each of said helical parts having a short leg and a long leg, the short leg of each of said helical parts abutting said stop and the long leg of each of said helical parts abutting one of said pallets.       

     The pallets and the long leg of the helical parts have mutual contact surfaces. It is preferred that these contact surfaces are convex and, more preferably, one or more of the contact surfaces is involute. Involute surface allows the surfaces to roll with each other rather than slide on each other. The rolling motion reduces spring wear and increases the life of the parts. Furthermore, by using the long leg and a pallet arrangement of the present Invention, the point of contact between the leg and the pallet can be varied. This means that the longer the leg the smaller the angular deflection of spring, which increases the life of the spring. 
     Preferably, the contact surface of the long leg of each of the helical parts is in rolling contact with the contact part of each of the pallets. 
     The inside wall of the outer elongated body side wall preferably has a recess which accommodates the movement of the pallets. 
     The pallets are preferably finger shaped, one side of which is curved and provides a contact surface. 
     The contact point between the pallets and the long leg of the helical part can be varied in location by varying the position of the pallet on the side wall of the inner elongated body and the length of the long leg so as to change the gear ratio. 
     The long leg of the helical part extends outward from the helical part and is transverse to the axis of helical part and parallel to the long axis of the outer elongated body. The short legs of the helical parts can be either connected to each other to form a bridge that abuts the stop or the short legs are not connected and each short leg abuts the stop. 
     If the short legs are not connected then two stops can be employed, one for each short leg. 
     Preferably, the bridge formed by the short legs is transverse to the long axis of the outer elongated body and parallel to the axis of the helical parts. Preferably, when the short legs are not connected, the short legs extend outward from the helical parts, transversely to the axis of the helical part and parallel to the long axis of the outer elongated body. 
     These and other aspects of the present invention may be more fully understood by reference to one or more of the following drawings and the detailed description thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a finger follower of the present invention with the valve stem, the cam, and the lash adjuster with a lost motion torsional spring device having two separate helical parts; 
         FIG. 2  is an exploded view of the finger follower of  FIG. 1 ; 
         FIGS. 3 and 4  illustrate the action of the lost motion torsional spring device of the finger follower of  FIG. 1  when the cam acts on the cam follower and the latch assembly has not been latched; and 
         FIGS. 5 and 6  illustrate the motion of the inner elongated body and the cam follower of the finger follower of  FIG. 1  when acted upon by the cam and when the latch is in the unlatched state; and 
         FIG. 7  illustrates a finger follower with a lost motion torsional spring device with two connected helical parts. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIGS. 1-6  illustrate finger follower  10  with lost motion torsional spring device  60  having two separate helical parts  62 ,  63 , while  FIG. 7  illustrates finger follower  84  with lost motion torsional spring device  90  with short legs  96  and  98  joined by bridge  100  and outer elongated body  86  with stop  88 . 
       FIG. 1  illustrates finger follower  10  which is acted on by cam  12 . Finger follower  10  pivots and is in contact with lash adjuster  14 . Finger follower  10  through its pivot action operates on valve stem  16  to open and close the valve in a cylinder of an internal combustion engine (not shown). Finger follower  10  has pivot point  18 , which is the point of contact between finger follower  10  and lash adjuster  14 . 
     Finger follower  10  comprises an outer elongated body  20  having a valve stem end  22 , a lash adjuster end  24 , and two elongated body side walls  26  and  28 . 
     First inner cavity  30 , in outer elongated body  20 , is defined by valve stem end  22 , lash adjuster end  24  and side walls  26  and  28 . Affixed to outer elongated body  20 , at its lash adjuster end  24 , are lost motion spring pins  32  and  34 . Each of the side walls  26  and  28  provide lost motion spring stops  36  and  38 . 
     As shown in  FIG. 2 , inner elongated body  40  is positioned in first inner cavity  30 . Inner elongated body  40  has a first end  42  which is pivotally attached to the valve stem end  22  of outer elongated body  20 , by pin  41  a second end  44  which is adjacent to lash adjuster end  24  and two inner elongated side walls  46  and  48 . Second inner cavity  50  is located in inner elongated body  42  and is defined by first end  42 , second end  44  and side walls  46  and  48 . 
     Two lost motion pallets  52  and  54  are affixed to side walls  46  and  48 . 
     A center cam follower  56  is mounted in second inner cavity  50 . 
     Latch assembly  58  forms part of outer elongated body  20 . Latch assembly  58  is a conventional latch assembly which is operated in a conventional manner in order to lock the inner elongated body  40  to outer elongated body  20 . 
     Lost motion torsional spring device  60  has two helical parts  62  and  63  positioned on pins  32  and  34  respectively. Each helical part  62 ,  63  has a short leg  64  and  66  which abut lost motion spring stops  36  and  38  respectively. Long legs  68  and  70  of helical parts  62 ,  63  extend into first inner cavity  30  and abut pallets  52  and  54  respectively. 
     As can be seen in  FIGS. 5 and 6 , long legs  68  and  70  have contact surfaces  72  and  74 . Contact surfaces  72  and  74  are each convex, and, more preferably are involute. 
     Pallets  52  and  54  have contact surfaces  76  and  78 . Contact surfaces  76  and  78  are convex, and more preferably, involute. Contact surface  72  contacts contact surface  76  and contact surface  74  contacts contact surface  78 . 
     As can be seen in  FIG. 4  both side walls  26  and  28  have recesses  80  and  82 , respectively. Recesses  80  and  82  provide clearance for the movement of pallets  52  and  54  as inner elongated body  40  pivots about its first end  42 . This pivoting action is visible in  FIG. 3  and  FIG. 4 . 
     The interaction between contact surfaces  72 ,  74 ,  76 , and  78  are shown in  FIGS. 5 and 6 . It is preferred that each of the contact surfaces are convex so that they do not interfere with one another, and more preferably, the contact surfaces are involute such that the contact between the surfaces  72 - 76  and  74 - 78  is a rolling contact not a sliding contact. 
     Lost motion springs  60  is positioned above the pivot point of finger follower  10 . 
     Preferably, pallets  52  and  54  are molded as part of inner elongated body  40 . Contact surface  76  to  78  can be specially treated to provide for good reduced wear between contact surfaces  72  and  74 . 
     Turning to  FIG. 7 , finger follower  84  has outer elongated body  20  with lost motion spring stop  88 . Lost motion torsional spring device  90  has helical parts  92  and  94  mounted on pins  32 ,  34  respectively. Short legs  96  and  98  are joined to form bridge  100 . Bridge  100  abuts stop  88 . Long legs  68 ,  70  of helical parts  92 ,  94  abut pallets  52 ,  54  of inner elongated body  40 . As can be seen, spring  90  is similar to spring  60 , except the orientation of short legs  96 ,  98  and the inclusion of bridge  100 . It is noted that stop  88  is the end of laten assembly  58 , but latch assembly  58  does not extend outward from body  20 , thus, bridge  100  does not interfere with the action of latch assembly  58 . 
     It will be noted that by locating lost motion torsional spring device  60 ,  90  above pivot point  18 , less weight is provided above the valve stem. Also, by positioning lost motion torsional spring device above the pivot point, the mass motion of inertia about the pivot point is improved. 
     Suitable lost motion torsional spring device are sized for the dynamic loads required by the system to maintain cam contact, based on the hinge point and mass moment of inertia of the system. 
     Alternatively, it will be seen that the contact point or points between long legs  68 ,  70  and pallets  52 ,  54  can be moved to increase or decrease the length of legs  68 ,  70  and the point where contact is made. The longer the length of legs  68 ,  70 , the less angular displacement of spring device  60 ,  90  and the less weary and longer life of spring device  60 ,  90 . To move the contact point farther away from lash adjuster end  24 , pallets  52  and  54  are moved on side wall  46 ,  48  towards end  42  of inner body  40 , while still maintaining the rolling contact between surfaces  72 ,  74 ,  76 ,  78 . This effects the gear ratio of the follower. 
     Although only a limited number of specific embodiments of the present Invention have been expressly disclosed, it is, nonetheless, to be broadly construed and not to be limited except by the claims appended hereto. 
     REFERENCE CHARACTERS 
     
         
           10  Finger follower 
           12  cam 
           14  lash adjuster 
           16  valve stem 
           18  pivot point of finger follower 
           20  outer elongated body 
           22  valve stem end 
           24  lash adjuster end 
           26  side wall 
           28  side wall 
           30  first inner cavity 
           32  pins 
           34  pins 
           36  lost motion spring stop 
           38  lost motion spring stop 
           40  inner elongated body 
           41  pin 
           42  first end of inner elongated body 
           44  second end of inner elongated body 
           46  side wall 
           48  side wall 
           50  second inner cavity 
           52  pallet 
           54  pallet 
           56  center cam follower 
           58  latch assembly 
           60  lost motion torsional spring 
           62  helical spring part 
           63  helical spring part 
           64  short leg 
           66  short leg 
           68  long leg 
           70  long leg 
           72  contact surface of leg 
           74  contact surface of leg 
           76  contact surface of pallet 
           78  contact surface of pallet 
           80  recess 
           82  recess 
           84  finger follower 
           88  lost motion spring stop 
           90  lost motion torsional spring 
           92  helical spring part 
           94  helical spring part 
           96  short leg 
           98  short leg 
           100  bridge