Patent Publication Number: US-9903233-B2

Title: Coupling pin anti-rotation for a switchable roller finger follower

Description:
BACKGROUND 
     The present disclosure relates to a switchable roller finger follower for a valve train of an internal combustion (IC) engine, and more particularly, to the coupling pin of a switchable roller finger follower (SRFF) that provides at least two discrete valve lift modes. 
     More stringent fuel economy regulations in the transportation industry have prompted the need for improved efficiency of the IC engine. Light-weighting, 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. 
     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 is formed 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 more 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. Three-step discrete valve lift systems can combine valve deactivation and cam profile switching strategies. 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, a 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 finger followers, 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. 
     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. 
     In most IC engine applications, switchable valve train components for cylinder deactivation in an electro-hydraulic system are classified as “pressure-less-locked”, which equates to: 
     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, 
     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 by a given stroke to an unlocked position, facilitating valve deactivation where the rotary camshaft motion is not translated to the valve. 
     “Pressure-less-unlocked” electro-hydraulic systems can be found in some cam profile switching systems that switch between a full or high valve lift and a partial or low valve lift, which equates to: 
     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, 
     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. 
     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. 
     Many coupling assembly designs utilize a coupling pin that is configured with a locking surface that engages or disengages another locking surface to enable different valve lift modes. In the case of the SRFF, the coupling pin moves longitudinally within a bore of one lever to engage or disengage another lever. In many instances the coupling pin contains a flat locking surface that engages a corresponding flat locking surface. Flat locking surfaces are used because of their increased contact area and thus lower stresses and resultant wear, as compared to other shaped interfaces. However, alignment of the flat locking surface of the locking pin with the corresponding flat locking surface is required to enable locking functionality. Therefore, a solution is needed to provide alignment or anti-rotation of the locking pin, such that its flat locking surface maintains alignment with a corresponding flat locking surface. Additionally, a solution is needed that can be applied to different known SRFF designs that facilitate valve deactivation, cam profile switching, or a combination of the two, with a compact arrangement. 
     SUMMARY 
     A coupling pin anti-rotation arrangement for multiple embodiments of a SRFF, capable of switching between two or more valve lift modes of operation, is provided. In a first example embodiment, the SRFF is capable of switching between a full valve lift mode and a no valve lift mode. In a second example embodiment, the SRFF is capable of switching between a full or high valve lift mode and a partial or low valve lift mode. Both embodiments comprise of an outer lever that has two arms that extend along longitudinal sides of an inner lever. The inner lever has a cavity in the center to house a roller, mounted by a transverse axle, which serves as a camshaft interface. The inner and outer levers are pivotably connected at one end, and lockably connected at an opposite end. When the inner lever is locked to the outer lever via a coupling pin located on one of the inner or outer levers, a first locked position is achieved, defining a first valve lift mode. When the coupling pin is longitudinally actuated within a coupling pin bore such that the inner lever is unlocked from the outer lever, a second unlocked position is achieved, defining a second valve lift mode. During the second valve lift mode, at least one lost motion resilient element or spring provides a force that acts upon one of the inner or outer lever during its arcuate movement relative to the other lever. The coupling pin has a longitudinal coupling projection with a first locking surface in the form of a flat, located on the other of the inner or outer levers, to engage a second locking surface in the form of a flat upon actuation of the coupling pin within the coupling pin bore. To facilitate alignment of the first and second locking surfaces, a first coupling pin-side anti-rotation flat is arranged on the longitudinal coupling projection of the coupling pin. An anti-rotation clip, arranged on the same lever as the coupling pin bore, has a first clip-side finger at a locking end. The first coupling pin-side anti-rotation flat is slidably guided by the first clip-side finger throughout its longitudinal movement within the coupling pin bore to ensure proper alignment of the first and second locking surfaces. A second clip-side finger can be arranged at the locking end of the anti-rotation clip to slidably guide a second coupling pin-side anti-rotation flat arranged on the longitudinal coupling projection of the coupling pin. The first and second clip-side fingers can be configured with guide surfaces that face one another and guide oppositely located first and second coupling pin-side anti-rotation flats. At least one attachment hook can be arranged on the anti-rotation clip at an end opposite the clip-side fingers. The at least one attachment hook can be engaged with an end of a coupling pin bore housing opposite a locking end to retain the anti-rotation clip. The first, second, or both clip-side fingers can also retain the anti-rotation clip, engaging with the locking end of the coupling pin bore housing. With the previously described retention features of the anti-rotation clip, easy installation and removal from the coupling pin bore housing is possible and can be further enhanced by use of an elastically deflectable material for the anti-rotation clip. Various locations of the coupling pin bore and anti-rotation clip will now be described for the first and second example embodiments. 
     The first example embodiment of the SRFF that applies the disclosed arrangement for coupling pin anti-rotation comprises an outer lever that includes the coupling pin bore and the anti-rotation clip. In a first, locked position, the first locking surface of the coupling pin is engaged with the second locking surface of the inner lever. In this first, locked position, the inner lever and outer lever rotate in unison about a hydraulic pivot element, resulting in a full valve lift mode. In a second, unlocked position, the first locking surface is disengaged with the second locking surface of the inner lever. In this second, unlocked position, the inner lever rotates independently of the outer lever, resulting in a no valve lift mode. The SRFF captured in the first embodiment is typically utilized to facilitate engine valve deactivation. 
     The second example embodiment of the SRFF that applies the disclosed arrangement for coupling pin anti-rotation comprises an inner lever that houses the coupling pin bore and the anti-rotation clip. In this example embodiment, the outer lever comprises at least one slider pad or roller to interface with at least one camshaft lobe. In a first, locked position, the first locking surface of the coupling pin is engaged with the second locking surface of the outer lever, resulting in a first valve lift mode. In a second, unlocked position, the first locking surface is disengaged with the second locking surface of the outer lever, resulting in a second valve lift mode. Both the first and second valve lift modes typically achieve different valve lifts that are greater than zero. The SRFF captured in the second example embodiment is typically utilized to facilitate cam profile switching. 
     Additional aspects of the disclosure that can be used alone or in various combinations are described below and in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a perspective view of a valve train system that includes a SRFF according to a first example embodiment of the disclosure with no valve lift and full valve modes of operation. 
         FIGS. 2A and 2B  are perspective views of the SRFF of  FIG. 1 . 
         FIGS. 3A and 3B  are perspective views of the outer lever of the SRFF of  FIGS. 2A and 2B . 
         FIGS. 4A and 4B  are perspective views of the inner lever of the SRFF of  FIGS. 2A and 2B . 
         FIG. 5  is a perspective view of an anti-rotation clip utilized in  FIGS. 2A through 3B . 
         FIG. 6  is a perspective view of a coupling pin contained within the SRFF of  FIGS. 2A, 2B, and 8 . 
         FIG. 7A  is a cross-sectional view of the SRFF of  FIGS. 2A and 2B  in a first, locked position. 
         FIG. 7B  is a cross-sectional view of the SRFF of  FIGS. 2A and 2B  in a second, unlocked position. 
         FIG. 8  is a perspective view of a SRFF according to a second example embodiment of the disclosure with high valve lift and low valve lift modes of operation. 
         FIG. 9  is a perspective view of a tri-lobe camshaft for the SRFF shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS 
     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. 
     Referring to  FIG. 1 , a perspective view of a SRFF  12  is shown within a valve train system  10  of an IC engine that includes a camshaft  11 , an engine valve  26  and a hydraulic pivot element  18 . The camshaft  11  rotationally actuates the SRFF  12  through a roller  22  interface about the hydraulic pivot element  18 , causing rotational lift provided by the camshaft  11  to be translated to linear valve lift. The SRFF  12  shown in  FIG. 1  captures a first example embodiment of a coupling pin anti-rotation arrangement, which will be described in detail with reference to  FIGS. 2A through 7B . 
       FIGS. 2A and 2B  show top-side and bottom-side perspective views of the SRFF  12 , respectively. The SRFF  12  is comprised of an outer lever  16  attached to an inner lever  14  by a pivot axle  13 . The outer lever  16  is configured with a valve interface  24  at a third end  21  and a hydraulic pivot element interface  20  at a fourth end  25 . 
     Referring now to  FIGS. 3A to 7B , a detailed explanation of the design and function now follows for the SRFF  12  captured in  FIGS. 1 through 2B . With specific reference to  FIGS. 3A through 4B , the inner lever  14  is configured with a first pivot aperture  64  on a first end  34  and the outer lever  16  is configured with second and third pivot apertures  15 A, 15 B on the third end  21 . The pivot axle  13  shown in  FIGS. 2A and 2B  is disposed within the first, second, and third pivot apertures  64 , 15 A, 15 B to pivotably connect the inner lever  14  to the outer lever  16 . The outer lever  16  has two outer arms  50 A, 50 B that extend along longitudinal sides  68 A, 68 B of the inner lever  14 . A cavity  61  within the inner lever  14  houses the roller  22  that interfaces with the camshaft  11  shown in  FIG. 1 . The roller  22  is connected to the inner lever  14  via a transverse axle pin  60  disposed within two axle apertures  70 A, 70 B of the inner lever  14 . Lost motion resilient elements or springs  54 A, 54 B are arranged on respective lost motion spring posts  52 A, 52 B of the outer lever  16 . Lost motion spring retainers  56 A, 56 B ensure containment of the lost motion springs  54 A, 54 B on their respective lost motion spring posts  52 A, 52 B during operation. The lost motion springs  54 A, 54 B are arranged to apply an upward force against lost motion spring landings  58 A, 58 B located on the inner lever  14  to bias the roller  22  of the inner lever  14  to an upper-most position. 
     With reference to  FIGS. 3A and 3B , a fourth end  25  of the outer lever  16  is configured with a coupling pin bore  66  that houses a coupling pin  40 . Now referencing  FIG. 6 , the coupling pin  40  is shown that is configured with a coupling projection  42 . The preferred material of the coupling pin  40  is steel, but other suitable materials are also possible. A first locking surface  44  is configured on the coupling projection  42  as a flat but can be of any suitable form for such a locking function. Adjacent to the first locking surface  44  is a first coupling pin-side anti-rotation flat  46 A. A second coupling pin-side anti-rotation flat  46 B can also be arranged opposite of the first coupling pin-side anti-rotation flat  46 A. With reference to  FIG. 4B , a second locking surface  62  is shown on the second end  35  of the inner lever  14 , which receives the first locking surface  44  of the coupling projection  42  of the coupling pin  40 . The second locking surface  62  is also formed as a flat but can be of any suitable form for such a locking function. 
     With reference to  FIG. 7A , the coupling pin  40  is shown in a first, locked position in which a coupling pin bias spring  38  is at a first compressed length L 1 . In this first, locked position, the inner lever  14  and the outer lever  16  pivot in unison about the hydraulic pivot element  18  (reference  FIG. 1 ), resulting in a full valve lift mode. 
     Now referencing  FIG. 7B , the coupling pin  40  is longitudinally displaced within the coupling pin bore  66 , defining a second, unlocked position in which the coupling bias spring  38  is at a second compressed length L 2 . The second compressed length L 2  of the second, unlocked position is less than the first compressed length L 1  of the first, locked position. In this second, unlocked position, the inner lever  14  is allowed to rotate about the pivot axle  13  during each camshaft rotation, resulting in an arcuate motion of the inner lever  14 , often termed lost motion or lost motion stroke, while the outer lever  16  remains stationary. 
     During the lost motion stroke it is necessary to prevent excessive rotation of the coupling pin  40  to ensure that the first locking surface  44  remains aligned with the second locking surface  62  of the inner lever  14 . If this does not occur, the coupling pin  40  will not be displaceable to the first, locked position, as only a small space or gap is present between the first and second locking surfaces  44 , 62 . While this space can be of any size, it is preferably in the range of 0.010 to 0.300 mm. Referring to  FIGS. 3A, 3B, 5 and 6 , in accordance with such an anti-rotation requirement of the coupling pin  40 , an anti-rotation clip  26  is arranged on the outer lever  16 . The anti-rotation clip  26  is configured with a first clip-side finger  28 A at a locking end  31  of the anti-rotation clip  26 . The first clip-side finger  28 A has a first guide surface  30 A that slidably guides a first coupling pin-side anti-rotation flat  46 A arranged on a longitudinal coupling projection  42  of the coupling pin  40 . A second clip-side finger  28 B having a second guide surface  30 B that faces the first guide surface  30 A can also be arranged at the locking end  31  of the anti-rotation clip  26  to slidably guide the second coupling pin-side anti-rotation flat  46 B. The first or second clip-side fingers  28 A, 28 B can engage with a locking end  49  of a coupling pin bore housing  48  to secure or retain the anti-rotation clip  26  to the outer lever  16 . To ensure that proper alignment of the first and second locking surfaces  44 , 62  is fulfilled, a small space or gap is present between the coupling pin-side anti-rotation flats  46 A, 46 B and the first and second guide surfaces  30 A, 30 B of the first and second clip-side fingers  28 A, 28 B. While this space can be of any size, it is preferably in the range of 0.010 to 0.500 mm. This space ensures a free, non-binding movement between the coupling pin  40  and first and second clip-side fingers  28 A, 28 B under all operating and size conditions, however, any rotation of the locking pin  40  will be limited by this space. For this reason, contact between either the first or second guide surface  30 A, 30 B and the respective coupling pin-side anti-rotation flats  46 A, 46 B may occur over a portion or the entirety of the coupling pin stroke, inclusive of the first, locked and second, unlocked coupling pin  40  positions. To further retain or secure the anti-rotation clip  26  to the outer lever  16 , a first attachment hook  32 A can be arranged on an end  33  of the anti-rotation clip  26  that is opposite to the first and second clip-side fingers  28 A, 28 B. The first attachment hook  32 A can engage with an end  51  of the coupling pin bore housing  48  that is opposite the locking end  49 . A second attachment hook  32 B (or more, if needed) can also provide further retention of the anti-rotation clip  26 . Given the previously described retention features of the anti-rotation clip  26 , easy installation and removal from the coupling pin bore housing  48  is possible and can be further enhanced by use of an elastically deflectable material for the anti-rotation clip  26 . 
     Referring now to  FIG. 8 , a SRFF  72  is shown that captures a second embodiment of a coupling pin anti-rotation arrangement. The SRFF  72  includes an outer lever  74  pivotably attached to an inner lever  76  via pivot shaft  78 . The inner lever  76  is configured with a roller  80  to interface with a first low-lift camshaft lobe  92  of a tri-lobe camshaft configuration  90  shown in  FIG. 9 . The outer lever  74  is configured with two high lift slider pads  75 A, 75 B that interface with second and third high-lift camshaft lobes  94 A, 94 B of the tri-lobe camshaft configuration  90 . The inner lever  76  is configured with a coupling pin bore (not shown) that houses the coupling pin  40  of the first example embodiment with the first locking surface  44  and adjacent coupling-side anti-rotation flats  46 A, 46 B, as shown in  FIG. 6 . An anti-rotation clip  86  is arranged on the coupling pin bore housing  83 . The coupling pin  40  moves longitudinally within the coupling pin bore of the inner lever  76  to engage and disengage a second locking surface  84  located on the outer lever  74 . Engagement of the first locking surface  44  of the coupling pin  40  with the second locking surface  84  of the outer lever  74  defines a first, locked position that corresponds with a first valve lift mode. Disengagement of the first locking surface  44  of the coupling pin  40  from the second locking surface  84  of the outer lever  74  defines a second, unlocked position that corresponds with a second valve lift mode. Typically the first valve lift mode is greater than the second valve lift mode, therefore, the first valve lift mode is often termed “full lift” or “high lift” and the second valve lift mode is often termed “low lift” or “partial lift.” While in either of the first or second valve lift modes, anti-rotation of the coupling pin  40  is achieved by one or both of the coupling pin-side anti-rotation flats  46 A, 46 B (reference  FIG. 6 ) being slidably guided by one or both clip-side fingers  88 A, 88 B arranged on a locking end  87  of the anti-rotation clip  86 . 
     The second example embodiment of this disclosure shown in  FIG. 8 , depicts a SRFF with two high lift slider interfaces  75 A, 75 B on the outer lever  74  and a low lift interface on the inner lever  76  in the form of the roller  80 . It would also be possible to have the high lift interface on the inner lever  76  in the form of a single interface and the low lift interface on the outer lever  74 , in the form of two interfaces. 
     Having thus described various embodiments of the present arrangement 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.