Abstract:
A system for selectively switching the action of a valve in an internal combustion engine includes a roller finger follower having a frame and a disengageable roller. A two-part axial pin for the roller axle is spring-loaded to urge the pin axially of the roller axle to disengage the first part of the pin from the follower frame and simultaneously disengage the second part of the pin from the roller axle. Thus the roller becomes detached from the frame and the follower cannot actuate its designated valve. The roller and pins are retained within the frame by at least one torsion spring. The pins may be controllably reinserted into the sides of the roller and frame to reconnect the roller to the frame by any of various electromechanical and/or hydraulic means. When used in conjunction with a camshaft having high lift and low lift cam lobes, the deactivated follower will then actuate its designated valve according to the profile of the low lift lobes, which may be a no lift profile.

Description:
CROSS-REFERENCE OF RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/204,622 filed May 16, 2000. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates to actuation mechanisms for mode-switching and deactivation of valves in internal combustion engines; more particularly, to such actuation mechanisms including a roller finger follower in the valve train of such an engine; and most particularly, to a system for controllably inserting and releasing an axial pin assembly in such a follower to alternately enable and prevent the roller from translating the eccentricity of a camshaft lobe into reciprocating motion of an engine valve. Such a system also may be adapted for selective switching between a low lift cam profile useful for low engine speeds and a high lift cam profile useful for high engine speeds. The low lift mode may include zero lift of the valve, i.e., deactivation thereof.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is known to improve the fuel efficiency of multi-cylinder internal combustion engines by controllably reducing the number of combustive cylinders during periods of low power demand. Systems are known, for example, for interrupting the action of an engine&#39;s valve train at one or more points in the engine&#39;s rotary cycle. Valve train interruption or modulation is especially desirable because it can cause the valves of the designated cylinder or cylinders to remain closed and thus can prevent consumption of fuel by those cylinders. The valve train may be controllably interrupted, for example, by known variable mechanisms linking the camshafts to their associated roller finger followers. See, for example, the relevant disclosures of U.S. Pat. Nos. 5,937,809 and 6,019,076.  
           [0004]    It is known that low lift, short duration cam profiles are capable of delivering good low rpm drivability, fuel economy, and emissions. High lift, long duration cam profiles are capable of providing improved engine breathing at higher engine speeds for increased power output. A valve in a valve train may be controllably switched between low lift and high lift profiles.  
           [0005]    All such mechanisms require input from specialized sensors in the valve train to sense, for example, the angular position of a camshaft at any given moment, and sensors to sense the rotational speed of the engine. These and other inputs are provided to an Engine Control Module (ECM) programmed to respond by modulating the action of, and in the extreme deactivating or reactivating, the valves of preselected cylinders. For simply deactivating valves, such an approach can be quite complex and expensive to fabricate and install.  
           [0006]    Another approach for interrupting the valve train is by use of special deactivatable lifters which can be made hydraulically compliant or non-compliant as desired. Such an approach can require complex and expensive hydraulic and electrical circuitry and controls.  
           [0007]    What is needed is a simple and inexpensive means for interrupting a valve train between a camshaft lobe and a roller finger follower.  
           [0008]    A related need is for a simple and inexpensive means for mode-switching a valve train between high lift and low lift valve actuation.  
         SUMMARY OF THE INVENTION  
         [0009]    Briefly described, a mode-switching valve train system in accordance with the invention includes a specialized roller finger follower having a frame and a roller disposed operationally between a camshaft lobe and a valve stem, the follower being tethered conventionally by lash adjustment means at an end opposite the engagement point with the valve stem. A two-part axial pin for the roller is spring-loaded to urge the pin axially of the roller such that the first part of the pin is withdrawn from engagement with the follower frame and simultaneously the second part of the pin is withdrawn from the roller into an opposite side of the frame. Thus the roller becomes detached from the frame and, in following the profile of the camshaft during rotation thereof, cannot cause the frame to actuate its designated valve; thus, the valve is deactivated. When the above-described camshaft lobe is a central high lift lobe and the camshaft is additionally provided with low lift cam lobes adjacent the central lobe, the low lift lobes may engage the frame when the roller is deactivated, causing the valve to follow the profile of the low lift lobes. Thus, a roller finger follower in accordance with the invention may be used for selectively switching between valve activation and deactivation and also for selectively switching between high lift and low lift valve opening modes.  
           [0010]    Preferably, the roller and pins are retained within the frame by at least one torsion spring. The two-part pin may be controllably reinserted into the sides of the roller and frame to reconnect the roller to the frame by the axial motion of any of various electromechanical and/or hydraulic means which may be disposed on-axis or off-axis of the two-part pin and roller. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    These and other features and advantages of the invention will be more fully understood and appreciated from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is an isometric view from above of a prior art roller finger follower;  
         [0013]    [0013]FIG. 2 is an isometric view from above of an improved roller finger follower in accordance with the invention;  
         [0014]    [0014]FIG. 3 is an exploded view of the roller finger follower shown in FIG. 2;  
         [0015]    [0015]FIG. 4 is a plan view of the roller finger follower shown in FIGS. 2 and 3, showing in cross-sectional view a hydraulic actuator for on-axis actuation of the roller finger follower;  
         [0016]    [0016]FIG. 5 is a view like that shown in FIG. 4, showing schematically a solenoid for electromechanical on-axis actuation of the roller finger follower;  
         [0017]    [0017]FIG. 6 is a plan view of an off-axis actuator, which may be either hydraulic or electromechanical, coupled by pivot arms to both an intake valve follower and an exhaust valve follower for a single cylinder, for simultaneous actuation thereof;  
         [0018]    [0018]FIG. 6 a  is a plan view like that shown in FIG. 6 of an off-axis actuator coupled by non-pivoting arms for simultaneous direct actuation of intake and exhaust valve followers;  
         [0019]    [0019]FIG. 7 is a plan view of a portion of a multi-cylinder assembly including a plurality of off-axis actuators like that shown in FIG. 6, showing roller finger followers in activated and deactivated states; and  
         [0020]    [0020]FIG. 8 is an isometric view from above of a complete assembly of off-axis actuators like that shown in FIG. 6, the assembly being configured for activation/deactivation of the roller finger followers for a three-cylinder bank of a V-6 engine.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    Benefits and advantages of a mode switching valve train system including a roller finger follower in accordance with the invention may be better appreciated by first considering a prior art roller finger follower.  
         [0022]    [0022]FIG. 1 shows a prior art roller finger follower  10  for translating the rotary motion of a camshaft lobe into reciprocating motion of a valve. The construction and disposition of follower  10  in an internal combustion engine is well known in the automotive art and thus is not described herein in detail except as needed to distinguish novel differences between a prior art follower and an improved follower in accordance with the invention. Follower  10  includes a frame  12  and a roller  14  rotatably disposed on an axial pin  16  fixed at opposite ends in bores  15  in sidewalls  17 , 19  of frame  12 . Typically, roller  14  is provided with a bearing  18  which may be a journal bushing or a roller or needle bearing. Frame  12  has a first socket formed on an underside thereof, the dome  20  of which is visible in FIG. 1, for pivotably receiving a conventional lash adjustment means (not shown) by which follower  10  is tethered to an engine. Frame  12  further has a pallet formed on the underside thereof (not shown) at an opposite end of frame  12  from dome  20  for receiving valve actuation means, for example, the stem of an engine valve (also not shown). In operation, the lash adjustment means urges roller  14  into constant contact with (“follows”) a camshaft lobe (not shown) during rotation thereof by engine driving means. As the eccentric valve-opening portion of the lobe passes over roller  14 , the follower  10  is caused to pivot on the lash adjustment means away from the cam axis, thus depressing the valve lifter and opening the valve. Similarly, as the eccentric valve-closing portion of the lobe passes over roller  14 , the follower  10  is caused to pivot on the lash adjustment means toward the cam axis, thus allowing the valve to be closed by a valve spring (not shown).  
         [0023]    Referring to FIGS. 2 and 3, an improved mode switching roller finger follower  10   a  is similar to prior art follower  10  in general shape and disposition within an engine, with the following novel improvements.  
         [0024]    Axial pin  16  is replaced with a hollow axle  16   a  rotatably supported by bearing  18  and housing a two-part axial pin assembly  22 , 24 . First pin  22  is disposed within axle  16   a  for detachably engaging bore  15  to rotatably support roller  14  at a first end. Pin  22  is provided with an enlarged portion  26  for engaging and retaining a coil spring  28  in compression between portion  26  and a feature  15  within axle  16   a , which spring urges pin  22  away from sidewall  17  and, when permitted, into disengagement from bore  15 . Shouldered second pin  24  is matably and coaxially disposed against portion  26  of pin  22  and is thereby urged by spring  28  into a shouldered retainer  29  in a boss  30  which is affixed to the side of frame  12   a  coaxially with bore  15  along axis  25 . An outer portion  32  of pin  24  extends through retainer  29  as an axial trigger for activating and deactivating follower  10   a.    
         [0025]    In operation, when trigger  32  is depressed into boss  30 , follower  10   a  is activated. Pin  24  is extended into axle  16   a  and in becoming so extended forces pin  22  into bore  15  and compresses spring  28 . Thus, roller  14  is rotatably supported on both sidewalls  17 , 19 , and follower  10   a  can function exactly as does prior art follower  10 .  
         [0026]    When permitted as described below, by removal of axial compressive force against trigger  32 , spring  28  forces pins  22 , 24  away from bore  15  until the shoulder on pin  24  engages the shoulder in retainer  29  which acts as a stop. The lengths of pins  22 , 24  are selected such that the interior end of pin  24  clears the end of axle  16   a  as the opposite end of pin  22  clears bore  15 , thus releasing both ends of axle  16   a  and roller  14  from support by frame  12   a . Pin  22  is retained within axle  16   a  and cannot engage either bore in sidewalls  17 , 19 . Preferably, tracks are formed, comprising channels  34 , for axle  16   a  and the bearing and roller in radial excursions away from axis  25 . Mode switching follower  10   a  is further provided with at least one, and preferably two, torsion springs  36  disposed coaxially on axle  16   a  and torsionally engaged with frame  12   a.    
         [0027]    In operation, when the roller is disengaged from the frame, as just described, the roller and pins are free to float in channels  34 . As the valve-opening portion of the cam lobe rotates past roller  14 , the roller and pins, following the lobe, are displaced along channels  34  away from axis  25 , compressing springs  36 . As the valve-closing portion of the cam lobe rotates past roller  14 , the roller and pins are returned along channels  34  by springs  36 . Thus the improved roller finger follower  10   a  is decoupled from the center cam lobe by the extension of trigger  32 , frame  12   a  does not follow the surface motion of the cam lobe, and the associated valve remains closed. When the camshaft is also provided with outer cam lobes (not shown), the outer lobes may ride on the top surfaces  66 , 68  of sidewalls  17 , 19  respectively, and roller finger follower  10   a  will thus follow the profiles of the outer cam lobes. See, for example, camshaft lobes  13  and  15  in FIG. 1 of U.S. Pat. No. 5,697,333, the relevant disclosure of which is herein incorporated by reference.  
         [0028]    For the purpose of disclosing actuator function in accordance with the invention, a cylinder valve deactivation application is herein discussed, although it should be understood that such actuation systems may similarly be used in a cam profile switching valve train.  
         [0029]    Trigger  32  may be actuated by any convenient axial-force-imposing means in response to a signal from an ECM in known fashion. Such a signal may be translated into an hydraulic or an electromechanical response. Referring to FIGS. 4 and 5, a linear actuator may be readily mounted on the engine adjacent to follower  10   a  to deliver axial force against trigger  32 . Such an actuator may be a hydraulic actuator  38 , for example, as shown in FIG. 4, having a piston  40  operable within a cylinder  42  and attached to an actuation plate  44  for mating with trigger  32 . Hydraulic actuator  38  is configured such that pressurized oil may enter an annular chamber  41  through a supply port  43 . The force exerted by the pressurized oil on piston  40  causes the piston to translate against the force of spring  47 . Such translation causes actuation plate  44  to be translated away from trigger  32 , allowing the roller to become detached from the frame of the switchable roller finger follower. When the supply of pressurized oil is removed, spring  47  exerts a force on piston  40  causing the piston to translate within cylinder  42 , thereby forcing the oil in chamber  41  to evacuate through supply port  43 . Piston  40  may translate until it is stopped by the surface of boss  45 .  
         [0030]    Alternatively, a conventional electromechanical solenoid  46  may be used as an actuator, as shown in FIG. 5. In either case, it is preferable that the actuator be provided with a return spring  47  having greater compressive force than spring  28  within follower  10   a  so that the fail-safe and engine-off position of the follower is in the valve-activating position with trigger  32  depressed, as shown in FIGS. 4 and 5. Thus the deactivating stroke of the actuator is in a direction away from the follower, allowing the follower to spontaneously become deactivated itself.  
         [0031]    In some engine applications, steric hindrance arises when the actuator is located coaxially on axis  25 , as shown in FIGS. 4 and 5, in that access to the bolts or studs securing the engine head to the engine block is impaired. This can present a significant problem in engine manufacture, where it is desirable to have the head fully assembled before attachment to the block. In such applications, off-axis actuation may be preferable.  
         [0032]    Referring to FIG. 6, a novel off-axis actuation system  49  is shown. A linear actuator  48 , which may be hydraulic or electromechanical, is disposed generally centrally of an engine head (not shown) between an intake valve follower  50  and an exhaust valve follower  52  for the same engine cylinder. Pivot arms  54 , 56  are provided with actuation plates  44  for engaging triggers  32  and are mounted on fixed pivot shafts  58  and are pivotably attached to an actuation shaft  44   a  extending from actuator  48 . A spring similar to spring  47 , as shown in FIG. 4 and described for actuators  38  and  46 , is incorporated in actuator  48 , either internally or externally, to bias arms  54  toward the followers so that they are activated to the default position. When shaft  44   a  is retracted by energizing of actuator  48 , arms  54  and  56  are simultaneously pivoted about pivot shafts  58 , releasing triggers  32  on followers  50  and  52 , as shown in FIG. 7, thereby deactivating the followers and their associated valves.  
         [0033]    Referring to FIG. 6 a , another off-axis actuation system  51  is shown. As in FIG. 6, linear actuator  48  is disposed generally centrally of an engine head (not shown) between an intake valve follower  50  and an exhaust valve follower  52  for the same engine cylinder. Like arms  54 , 56 , arms  54   a , 56   a  are provided with actuation plates  44  for engaging triggers  32  but are not mounted on fixed pivot shafts and are not pivotably attached to an actuation shaft  44   a  extending from actuator  48 . Rather, arms  54   a , 56   a  form a solid unit which engages triggers  32  directly in response to retractive action of actuator  48 . Preferably, the arms are provided with a guiding mechanism which may take the form of guides  53  extending along opposite sides of actuator  48  and urged thusly by a return spring  55  to bias arms  54   a , 56   a  toward the followers so that they are activated to the default position.  
         [0034]    In FIGS. 7 and 8, an assembly  60  comprising a plurality of off-axis actuator systems  49  is shown for installation onto an engine for deactivation of a plurality of cylinder valves of an internal combustion engine  57 . Actuators  48  and pivot shafts  58  are fixed to a shaped baseplate  62  having, for example, openings  64  for access to spark plug towers in the engine head. Assembly  60  is configured for deactivation of four valves per cylinder of a three-cylinder head, as may be used in a V-6 style engine (not shown); that is, actuators  48 - 1  and actuation plates  44   a - 1  control actuation of the four valves of a first cylinder, actuators  48 - 2  and plates  44   a - 2  the valves of a second cylinder, and actuators  48 - 3  and plates  44   a - 3  the valves of a third cylinder.  
         [0035]    It will be apparent to one of ordinary skill in the art that a valve train mode switching system including a roller finger follower, as illustrated and described herein, and many of its features, could take various forms as applied to other applications and the like. While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.