Patent Application
20080283003
The present invention relates to roller finger followers used for variable valve actuation in overhead cam type internal combustion engines; and more particularly, to a roller finger follower assembly having a body supportive of an axle shaft for dual outboard rollers for following a corresponding pair of cam lobes, and a central slider arm for following a central cam lobe between the pair of lobes; and most particularly, to such an assembly wherein the slider is pivotably mounted on the axle shaft.
Roller Finger Followers (RFFs) are widely used in overhead cam internal combustion engines to sequentially open and close the cylinder intake and exhaust valves. In a typical application, the RFF assembly serves to transfer and translate rotary motion of a camshaft eccentric lobe into a pivotal motion of the RFF assembly to thereby open and close an associated valve.
It is known that, for a portion of the duty cycle of a typical multiple-cylinder engine, the performance load can be met by a functionally smaller engine having fewer firing cylinders, and that at low-demand times fuel efficiency can be improved if one or more cylinders of a larger engine can be withdrawn from firing service. It is also known that at times of low torque demand, valves may be opened to only a low lift position to conserve fuel, and that at times of high torque demand, the valves may be opened wider to a high lift position to admit more fuel. It is known in the art to accomplish this by de-activating a portion of the valve train associated with pre-selected cylinders in any of various ways. One way is by providing a special two-step RFF assembly having a variably activatable and deactivatable central slider arm which may be positioned for contact with a high lift lobe of the camshaft. Such a two-step RFF typically is also configured with rollers disposed at each side of the slider arm for contact with low lift lobes of the cam shaft on either side of the high-lift lobe. Thus, the two-step RFF causes low lift of the associated valve when the slider arm of the RFF is in a deactivated (unlatched) mode, and high lift of the associated valve when the slider arm of the RFF is an activated (latched) mode to transmit motion of the high lift lobe of the camshaft.
A typical prior art two-step roller finger follower is disclosed in U.S. Pat. No. 6,755,167 B2, issued Jun. 29, 2004, the relevant disclosure of which is incorporated herein by reference. In this roller finger follower, an elongate body having first and second side members defines coaxially disposed shaft orifices. A pallet end and a socket end interconnect with the first and second side members to define a central slider arm aperture and a latch pin channel. The socket end is adapted to mate with a mounting element such as an hydraulic lash adjuster, and the pallet end is adapted to mate with a valve stem, pintle, lifter, or the like. A slider arm for engaging a high-lift cam lobe is disposed in the slider arm aperture and has first and second ends, the first end of the slider arm being pivotally mounted to the pallet end of the body and the second end defining a slider tip for engaging an activation/deactivation latch pin. The latch pin is slidably disposed in the latch pin channel, the latch pin having a nose section for selectively engaging the slider tip. A spool-shaped roller comprising a shaft and opposed roller elements fixedly attached to ends of the shaft is rotatably disposed in the shaft orifices, the roller being adapted to cause the RFF body to follow the surface motion of a low-lift cam lobes. Preferably, the shaft is journalled in roller or needle bearings which extend between and through both the first and second shaft orifices, being thus exposed to normal copious oil flow through central regions of the RFF. A coil torsion spring mounted on the slider arm pivot pin urges the slider into continuous contact with the central cam lobe.
US Published Patent Application No. 20060249110, the relevant disclosure of which is incorporated herein by reference, discloses a similar two-step RFF assembly except that the latch pin channel and latch pin are inclined to the pivot axis of the slider arm to improved latching reliability, and the coil torsion spring is replaced by a compression coil spring disposed within a well in the slider arm.
See also U.S. Pat. No. 6,925,978, the relevant disclosure of which is incorporated herein by reference.
A drawback of all such prior art two-step RFF assemblies is that the mass of the central slider, and therefore the moment of rotational inertia, is undesirably high, which increases the force requirements of the lost motion and valve springs.
Another drawback is that the overall volume, and therefore the engine space consumed, is undesirably large.
Still another drawback is that the range of lost motion of the central slider is constrained by practical limits of mechanical strength imposed by the arcuate slot in the central slider for accommodating the axle of the low-lift rollers.
Still another drawback is that the number of components is undesirably large, resulting in relatively high component manufacturing and assembly costs.
Still another drawback is that provision for a rotational stop to limit leakdown of an associated HLA requires special manufacturing and assembly components and procedures.
International Publication No. WO 2007/035673 A2 discloses a finger follower assembly having a central roller follower for following a central cam lobe, the central roller follower being mounted on a shaft passing through the assembly body and supporting a linked pair of lateral slider followers for following dual cam lobes on either side of the central lobe. The lateral slider followers are mounted eccentrically on the shaft and thus may be rotated between a latched high-lift (valve actuating) position and an unlatched low-lift (valve deactivating or lost motion) position. The lateral slider followers are latched and unlatched by a hydraulic piston latching mechanism in the assembly body. Thus, the central roller follower is engaged for low-lift or no-lift valve events, and the lateral sliders are engaged for high-lift valve events and are disengaged for low-lift or no-lift valve events.
A serious drawback of this two-step RFF assembly is that it requires complicated component shapes and features to implement the locking function. Further, packaging and assembly of the slider bias springs is difficult and problematic.
What is needed in the art is a simplified two-step RFF assembly having fewer components, lower mass, lower volume, and greater range of lost motion than comparable prior art RFF assemblies.
It is a principal object of the present invention to reduce the cost, complexity, and mass of a two-step RFF assembly.
It is also an object of the invention to reduce the volume and rotational inertia of a two-step RFF assembly.
Briefly described, a roller finger follower for use in conjunction with a cam shaft of an internal combustion engine comprises an elongate body having first and second side members defining coaxially disposed shaft orifices. A pallet end and a socket end interconnect with the first and second side members to define a slider arm aperture and a latch pin channel. The socket end is adapted to mate with a mounting element such as an hydraulic lash adjuster, and the pallet end is adapted to mate with a valve stem, pintle, lifter, or the like.
A spool-shaped roller comprising a shaft and opposed roller elements attached to the shaft is disposed in the shaft orifices, the rollers being adapted to follow the surface motion of the low-lift cam lobes. Preferably, the shaft is journalled in roller or needle bearings which extend between and through both the first and second shaft orifices, being thus exposed to normal copious oil flow through central regions of the RFF.
A slider arm for engaging a high-lift cam lobe is disposed in the slider arm aperture and is pivotally mounted on a common axis with the roller shaft and includes a slider tip for engaging an activation/deactivation latch pin. The latch pin is slidably and at least partially disposed in the latch pin channel and has a nose section for extending from the channel to selectively engage the slider tip, to switch modes of the RFF assembly.
The foregoing and other objects, features, and advantages of the invention, as well as presently preferred embodiments thereof, will become more apparent from a reading of the following description in connection with the accompanying drawings in which:
The benefits and advantages of a two-step RFF assembly in accordance with the present invention may be better appreciated by first considering a prior art two-step RFF assembly.
Referring to
Body assembly 16 includes elongate body 26 and roller bearing 28 disposed in bearing orifices 30. Elongate body 26 includes a slider arm aperture 32 bounded by body side walls 34 defining bearing orifice 30 therethrough. The diameter of bearing orifice 30 is sized to press-fittedly receive roller bearings 28. A cross-shaft 36 is rotatably disposed in bearing 28 and is supportive of roller 38 on the end thereof for following a low-lift cam lobe. Of course, a second body sidewall, bearings, roller, and the like are all present in an actual RFF assembly but are not visible in the cross-sectional view shown in
Slider arm assembly 18 includes slider arm 40 and slider shaft 42, having mutual axes 43, for pivotably attaching arm 40 to body 26. Slider arm 40 defines slider surface 44 for following a high-lift cam lobe, and further includes slider tip 46 and elongated roller shaft clearance aperture 48. It should be noted that prior art slider arm assembly, because it pivots from shaft 42, includes substantial mass between aperture 48 and shaft 42 which exists for no purpose other than to allow the slider arm assembly to pivot from a pivot axis disposed over valve stem 11 and pallet end 12. It is an important benefit of the improved two-step RFF assembly as disclosed and claimed herein that most of this portion of a slider arm assembly is eliminated and therefore the rotational mass of an improved slider arm assembly, as described below, is substantially reduced.
In prior art RFF 10, latch pin axis 54 is substantially perpendicular to, and passes through, pivot pin axis 43. Thus axis 54 lies on a radius 55 of the rotational arc of slider arm 40 (i.e., axis 54 forms an included angle 57 of 180° with an extension of radius 55), causing slider tip 46 to be traveling in a direction substantially orthogonal to axis 54 at the point of engagement with latch pin 52.
Referring now to
Referring now to
Improved RFF assembly 110 includes body assembly 116, central slider arm 140, spool roller assembly 120, lost motion spring 122, and latch assembly 124.
Body assembly 116 includes elongate body 126 and roller bearings 128. Elongate body 126 includes a slider arm aperture 132 bounded by body side walls 134 defining bearing orifices 130 formed in bosses 131 of sidewalls 134. The diameter of bearing orifice 130 is sized to press-fittedly receive roller bearings 128. A cross-shaft 136 is rotatably disposed in bearings 128 and is supportive of rollers 138 on the ends thereof for following first and second outboard low-lift cam lobes 92 (
Slider arm 140 defines a slider surface 144 for following high-lift cam lobe 94, and further includes slider tip 146 (
Referring now to
In operation, during lost motion slider arm 140 pivots about axis 161 of shaft 136, and cam lobe 94 engages slider arm 140 on surface 144b. During valve actuation, of course, slider arm 140 does not rotate about axis 161 but rather is latched at lip 146 to latch pin 161 and thus is integral with RFF body 126.
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.
