The present invention relates to mechanisms for altering the actuation of valves in internal combustion engines; more particularly, to finger follower type rocker arm assemblies having means for changing between normal and no valve lifts; and most particularly, to a two-step roller finger follower (RFF) assembly having a center reciprocating member disposed in a finger follower rocker arm body for reciprocating motion in the direction of lift between normal-lift and no-lift positions, and having a latching mechanism operative in an orthogonal bore in the finger follower body for latching and unlatching the reciprocating member to and from the finger follower body to shift between high lift and no lift modes, the latching mechanism being actuated by a latching spring and deactuated by engine oil supplied through a hydraulic lash adjuster.
Variable valve activation mechanisms for internal combustion engines are well known. It is known to lower the lift, or even to provide no lift at all, of one or more valves of a multiple-cylinder engine during periods of light engine load. Such deactivation can substantially improve fuel efficiency.
Various approaches have been disclosed for changing the lift of valves in a running engine. One known approach is to provide a deactivation mechanism within the hydraulic lash adjuster (HLA) upon which a cam follower rocker arm pivots. Such an arrangement is advantageous in that it can provide variable lift from a single cam lobe by making the HLA either competent or incompetent to transfer the motion of the cam eccentric to the valve stem. A shortcoming of providing deactivation directly by the HLA is that because the cam lobe actuates the rocker near its longitudinal center point, the variation in lift produced at the valve-actuating end can be only about one-half of the extent of travel of the HLA deactivation mechanism.
Another known approach is to provide a deactivation mechanism in the roller finger follower itself, such as that disclosed in U.S. Pat. No. 6,604,498. In the mechanism disclosed, a two-part roller axle serves to selectively latch and delatch the roller from the body of the follower. The actuating mechanism needed to operate the deactivation mechanism resides adjacent one side of the roller finger follower body to act against an end of the two-part roller axle. For that reason, the mechanism occupies a substantial amount of space and can be cumbersome.
What is needed is a compact valve activation mechanism contained within a roller finger follower that is capable of deactivating an associated valve resulting in zero lift of the associated valve.
Briefly described, a roller finger follower rocker arm assembly in accordance with the invention includes a follower body having a socket at a first end for engaging a conventional hydraulic lash adjuster as a pivot means, and having a pad at a second and opposite end for engaging a valve stem or lifter means. A passage through the follower body in the direction of actuation by an engine camshaft is slidingly receivable of a reciprocating member. A transverse bore in the reciprocating member intersects elongate slots in the body on either side of the member. A shaft defining an axle is rotatably supported in the bore of the reciprocating member and extends through the bore and the slots in the body. First and second rollers are attached to the axle shaft outboard of the body for following identical first and second laterally-disposed eccentric portions of a cam lobe that straddle the body. The reciprocating member, axle shaft, bearings, and rollers define a center member sub-assembly. A base circle central portion of the cam lobe extends axially across the body between the eccentric portions. A latching mechanism selectively locks the body to the center member sub-assembly such that the entire follower follows the motion of the eccentric portions of the cam lobe. The reciprocating member itself does not make contact with the cam lobe and functions only as a link between the latching mechanism and the rollers. Preferably, the latching mechanism is lockingly engaged into the reciprocating member by a latching spring and is disengaged from the reciprocating member by the force of pressurized oil, controllably supplied through a passage from the head of the hydraulic lash adjuster, which overcomes the latching spring. A lost motion spring disposed between the reciprocating member and the body urges the rollers of the center member sub-assembly into continuous contact with the eccentric portions of the cam lobe. When the latching mechanism is disengaged from the reciprocating member, as by interrupting the oil supply, the center member sub-assembly reciprocates within the follower body as the rollers continue to follow the eccentric portions of the cam lobes in lost motion. Means is provided for limiting axial growth of the HLA during deactivation mode of the rocker arm assembly.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
A roller finger follower assembly 10, 10′ for valve deactivation in accordance with the invention includes a follower body 12 having a first end 14 having means for receiving the head of a hydraulic lash adjuster 16 for pivotably mounting assembly 10, 10′ in an engine 18. The receiving means is preferably a spherical socket 20. A second and opposite end 22 of follower body 12 is provided with a pad 24, preferably arcuate, for interfacing with and actuating a valve stem 26 of an engine valve 27, such as a cylinder intake valve for engine 18. Body 12 is provided with a first passage 28 therethrough, passage 28 being generally cylindrical and having sliding surface 29 for slidably receiving a partially-cylindrical mating portion 30 of a reciprocating member 32 having a bore 34 transverse of passage 28. Passage 28 defines first and second body sidewalls 36,38. Sidewalls 36,38 are provided with flat bosses 40 on the outer surfaces, and elongated openings 42,44 are formed in the sidewalls and bosses. A shaft 46 defining an axle is rotatably supported in bore 34 as by needle bearings 48 and extends through both of openings 42,44. Follower rollers 50,52 are fixed onto axle shaft 46 on opposite ends thereof as, for example, by press fit. Taken together, reciprocating member 32, bearings 48, axle shaft 46, and rollers 50,52 define a center member sub-assembly 54 for variable engagement by and sliding within body 12.
Reciprocating member 32 further includes an head portion 56 extending toward first and second ends 14,22 of body 12 to define, respectively, a latching surface 58 and a spring seat 60. Second end 22 is provided with a well 62 for receiving a lost-motion spring 64 disposed between end 22 and spring seat 60.
First end 14 is further provided with a latching mechanism 66, as best shown in
Referring to
Referring now to
Referring to
While assemblies 10, 10′ are in valve-deactivation mode, body 12 is ungrounded at the HLA end 14. Further, the HLA is under reduced axial load from the rocker arm assembly while simultaneously being supplied with high-pressure oil. Consequently, if body 12 is unconstrained, there will be a tendency for the HLA to expand axially, and any such expansion results in mis-positioning body 12, preventing later re-engagement with center member sub-assembly 54. Thus, it is important to prevent unconstrained growth of the HLA during valve deactivation mode. Two embodiments for preventing HLA growth are shown in
Referring to
Referring to
In the embodiments shown, latch member 76 is activated by supplying pressurized oil through oil passages internal to the body of the roller finger follower. It is understood that the present invention also contemplates that the latch member can be a simple spring-biased pin with an end portion protruding axially from body bore 68. An external actuator would act on the protruding end portion to move latch member 76 from a latched position to an unlatched position.
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.