Switching Finger Follower Assembly
A finger follower assembly (30) for variably activating a valve of an internal combustion engine having a camshaft with at least one lobe (40). The finger follower assembly includes a follower body (54), a shaft (78), a cam follower (56), and a latching mechanism (58). The cam follower is supported by the shaft and is configured for engagement with the at least one lobe. The cam follower is configured to pilot on the camshaft to maintain an alignment of the cam follower with respect to the at least one lobe. The latching mechanism selectively latches and unlatches the cam follower to the follower body to provide first valve lift capability and a second valve lift capability.
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This application claims priority to U.S. Provisional Patent Application No. 60/718,120, filed Sep. 16, 2005, the entire contents of which are hereby incorporated by reference herein.
BACKGROUNDThe present invention relates to mechanisms for altering the actuation of valves in internal combustion engines, and more particularly to finger follower type rocker arms for changing between high and low valve lifts.
Variable valve activation (VVA) mechanisms for internal combustion engines are known. It is known to lower the lift of one or more valves of a multiple-cylinder engine, especially intake valves, during periods of light engine load. Such deactivation can improve fuel efficiency.
Various approaches have been disclosed for changing the lift of valves in a running engine. One approach is to provide an intermediary cam follower arrangement which is rotatable about the engine camshaft and is capable of changing both the valve lift and timing. In such an approach, the camshaft typically includes both high-lift and low-lift lobes for each such valve. Such an arrangement can be complicated and costly to manufacture and difficult to install during engine assembly.
Another known approach is to provide a deactivation mechanism in 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 at the HLA end of a rocker arm 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.
Still another known approach is to provide a deactivation mechanism in the valve-actuating end of a rocker arm cam follower (opposite from the HLA pivot end) which locks and unlocks the valve actuator portion from the follower body. Unlike the HLA deactivation approach, this approach typically requires both high-lift and low-lift cam lobes to provide variable lift.
Another known approach is to provide a rocker arm cam follower with a finger body having a first cam follower positioned within the finger body and a secondary cam follower. In some designs, the first cam follower is selectively moveable relative to the finger body and in other designs the secondary cam followers are selectively moveable relative to the finger body. The moveable members generally are axially moveable or pivot about a secondary axis which adds complexity to the design or fails to provide smooth motion.
SUMMARY OF THE INVENTIONIn one embodiment the invention provides a finger follower assembly for variably activating a valve of an internal combustion engine having a camshaft with at least one lobe. The finger follower assembly includes a follower body, a shaft, a cam follower and a latching mechanism. The follower body has a first end portion configured to couple to the engine, a second end portion configured to couple to the valve of the engine, and an aperture formed in the follower body between the first and second end portions. The shaft is coupled to the follower body and transverses the aperture. The cam follower is supported at least partially within the aperture by the shaft and is configured for engagement with the at least one lobe. The cam follower is configured to pilot on the camshaft to maintain an alignment of the cam follower with respect to the at least one lobe. The latching mechanism selectively latches and unlatches the cam follower to the follower body to provide a first valve lift capability and a second valve lift capability.
In another embodiment the invention provides the follower body having a first end portion configured to couple to the engine, a second end portion configured to couple to the valve of the engine, and an aperture formed in the first end portion. The latching mechanism includes a base portion, a piston movable relative to the base portion between an extended position and a retracted position, and a biasing member. The biasing member is coupled between the base portion and the piston to bias the piston toward the retracted position, and the base portion, the piston, and the biasing member are at least partially located within the aperture.
In yet another embodiment the invention provides the latching mechanism having an engagement surface and the cam follower having an engagement surface configured to engage the engagement surface of the latching mechanism. At least one of the engagement surfaces is at least partially convex.
In yet another embodiment the invention provides the latching mechanism at least partially defining a fluid chamber, and the finger follower assembly further including a vent passageway formed in the first end portion of the follower body and providing selective fluid communication between the fluid chamber and an outer surface of the follower body.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. In addition, the invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. Certain terminology, for example, “top”, “bottom”, “right”, “left”, “front”, “frontward”, “forward”, “back”, “rear”, “rearward”, “upwardly” and “downwardly” is used in the following description for relative descriptive clarity only and is not intended to be limiting.
DETAILED DESCRIPTIONReferring to
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Referring to FIGS. 3 and 5-8, the lateral follower 80 has a body portion 90 with a through bore 92 that receives the shaft 78 to couple the lateral follower 80 to the follower body 54. The lateral follower 80 pivots or rotates about the shaft 78 and is movable along the shaft 78 in a direction parallel to the shaft axis 79.
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The illustrated lateral follower 80 is integrally formed as a single piece, such as by casting, molding, machining and the like. In other constructions, the lateral follower 80 can be a two-piece design, such that the first and second contact portions are separate components. In such constructions, the contact portions and can be interconnected by a member such that the contact portions are coupled for co-rotation about the shaft 78 and movement along the shaft axis 79.
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Because the lateral follower 80 pilots in this manner on the central lobe 40, the lateral follower 80 and central follower 82 remain aligned with the cam assembly 38 regardless of the manufacturing variations or thermal variations that may change the position of the cam assembly 38. Such as feature allows the widths W4 and W5 of the contact surfaces 106 and 108 to be maximized such that the widths W4 and W5 of the contact surfaces 106 and 108 are generally equal to the width of the perimeter surfaces 46 of the lateral lobes 42 and 44, respectively, and the contact surfaces 106 and 108 generally contact the lateral lobes 42 and 44, respectively, along their entire width W4 and W5. Generally, it is desirable to increase the width of the contact between the lateral lobes 42 and 44 and the contact surfaces 106 and 108 so that the lateral follower 80 is capable of carrying a larger valve lift load. Because the lateral follower 80 can move along the shaft 78 in response to a change in position of the cam assembly 38, the lateral lobes 40 and 42 and both of the contact surfaces 106 and 108 remain aligned to facilitate contact along substantially the entire width of the contact surfaces 106 and 108.
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Referring to FIG. 1 and 14-16, oil enters the finger follower assembly from the lash adjuster 50 and passes through an aperture 144 between the socket 64 and the bore 66, and then passes through the slot 138 in the piston 120. When low lift of the engine valve 52 is desired, the oil supplied to the finger follower 30 is at a relatively low pressure. Therefore, the biasing member 122, which has a natural tendency to expand in the illustrated construction, retains the piston 120 in the unlatched or retracted position (
With the piston 120 in the unlatched position, the high lift or lateral lobes 42 and 44 will contact surfaces 106 and 108 of the lateral follower 80 and cause a pivoting force on the lateral follower 80. In the unlocked condition, the lateral follower 80 simply pivots about the shaft axis 79 without imparting any significant force on the finger body 54. The lateral follower 80 is biased toward the lateral lobes 42 and 44 by the biasing member 116 and therefore the contact surfaces 106 and 108 generally remain in contact with the lateral lobes 42 and 44. Meanwhile, the central or low lift lobe 40 contacts the central follower 82 to cause the outer race 86 to rotate about the shaft 78. The lift of the valve 52 is controlled by the low lift lobe 40 through the central follower 82.
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Referring to FIGS. 1 and 17-19, when high lift of the engine valve 52 is desired, the oil supplied from the lash adjuster 50 increases. Once the oil pressure is at a sufficient pressure to compress the biasing member 122, the piston 120 moves from the retracted or unlatched position (
Referring to FIGS. 1 and 17-19, in the extended position the locking projection 130 of the piston 120 extends into the aperture 94 of the lateral follower 80 thereby interconnecting the lateral follower 80 and the follower body 54. Thus, as the lateral or high lift lobes 42 and 44 contact the lateral follower 80 the finger follower assembly 30 pivots on the lash adjuster 50 to provide relatively high lift of the engine valve 52. Meanwhile, a limited amount of oil is allowed to escape from the bore 126 of the piston 120 through the vent apertures 136 to provide lubrication for the lateral follower 80, the central follower 82, and the cams 40, 42, and 44.
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The illustrated latching mechanism 258 is of a slightly different construction from the latching mechanism 58 described above. The biasing member 322 is of a different configuration having a generally cylindrical coil diameter instead of the tapered diameter of the biasing member 122. Additionally, hooked ends 322a and 322b engage respective pins 379a and 379b that are coupled to the end cap 326 and the piston 320, respectively.
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The vent passageway 382 is in fluid communication with a fluid chamber 381 defined by the end cap or base 326, the bore 328 of the piston 320, and the bore 266 of the follower body 254 depending on the location of the piston 320. A plug 388 is located within the vent passageway 382 to substantially prevent fluid communication through the vent passageway 382 past the plug 388.
The secondary passageway 384 is adjacent the vent passageway 382. As best seen in
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In the illustrated construction, the tertiary passageway 386 is generally normal to the vent passageway 382 and the secondary passageway 384. The tertiary passageway 386 provides fluid communication between the vent passageway 382, the secondary passageway 384, and the outside of the finger follower 230.
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Various features and advantages are set forth in the following claims.
Claims
1. A finger follower assembly for variably activating a valve of an internal combustion engine having a camshaft with at least one lobe, the finger follower assembly comprising:
- a follower body having a first end portion configured to couple to the engine, a second end portion configured to couple to the valve of the engine, and an aperture formed in the follower body between the first and second end portions;
- a shaft coupled to the follower body that transverses the aperture;
- a cam follower supported at least partially within the aperture by the shaft and configured for engagement with the at least one lobe, the cam follower configured to pilot on the camshaft to maintain an alignment of the cam follower with respect to the at least one lobe; and
- a latching mechanism for selectively latching and unlatching the cam follower to the follower body to provide a first valve lift capability and a second valve lift capability.
2. The finger follower assembly of claim 1, wherein the cam follower is movable within the aperture in a direction parallel to a longitudinal axis of the shaft.
3. The finger follower assembly of claim 1, wherein the camshaft includes a central lobe and a lateral lobe adjacent a side of the central lobe, wherein the cam follower is a lateral follower configured to pilot on the central lobe, the finger follower assembly further comprising a central follower configured for engagement with the central lobe.
4. The finger follower assembly of claim 3, wherein the central follower is rotatably supported at least partially within the aperture by the shaft.
5. The finger follower assembly of claim 3, wherein the central follower is coupled with the lateral follower such that movement of the lateral follower with respect to the valve causes movement of the central follower.
6. The finger follower assembly of claim 3, wherein the central lobe includes a perimeter surface that contacts the central follower and a side wall portion that engages the lateral follower to pilot the lateral follower on the camshaft.
7. The finger follower assembly of claim 6, wherein the lateral follower includes a first contact surface configured to engage the lateral lobe and a second contact surface substantially normal to the first contact surface and configured to engage the side wall portion of the central lobe.
8. The finger follower assembly of claim 1, wherein the camshaft includes a first lobe and a second lobe, wherein the first lobe is configured to engage the cam follower, and wherein the cam follower includes a contact surface configured to contact the second lobe to pilot the cam follower.
9. The finger follower of claim 1, wherein the cam follower defines a body portion located at least partially within the aperture, the body portion having a width that is less than a width of the aperture such that the cam follower can move with respect to the follower body in a direction parallel to a longitudinal axis of the shaft.
10. The finger follower assembly of claim 1, wherein the latching mechanism includes a latching member having an engagement surface, the latching member selectively interconnects the cam follower and the follower body, and wherein the cam follower includes an engagement surface that at least partially defines an aperture that receives the latching mechanism, and wherein at least one of the engagement surfaces is at partially convex.
11. The finger follower assembly of claim 10, wherein the engagement surface of the cam follower is at least partially convex.
12. The finger follower assembly of claim 1, wherein the cam follower is integrally formed as a single component.
13. A finger follower assembly for variably activating a valve of an internal combustion engine, the finger follower assembly comprising:
- a follower body having a first end portion configured to couple to the engine, a second end portion configured to couple to the valve of the engine, and an aperture formed in the first end portion;
- a cam follower supported by the follower body; and
- a latching mechanism operable to selectively engage and disengage the cam follower to provide a first valve lift capability and a second valve lift capability, the latching mechanism including, a base portion, a piston movable relative to the base portion between an extended position and a retracted position, and a biasing member coupled between the base portion and the piston to bias the piston toward the retracted position, and wherein the base portion, the piston, and the biasing member are at least partially located within the aperture.
14. The finger follower assembly of claim 13, wherein the biasing member is a tapered spring.
15. The finger follower assembly of claim 13, wherein the aperture has a generally uniform inner dimension.
16. The finger follower assembly of claim 15, wherein the aperture is a cylindrical bore having a generally constant diameter.
17. The finger follower assembly of claim 13, wherein the base portion includes a tang, wherein the piston includes a slot, and wherein the tang is received within the slot of the piston to provide for a limited amount of rotation of the piston with respect to the follower body.
18. The finger follower assembly of claim 13, wherein a portion of the piston is located within the aperture, and wherein the portion of the piston has a generally constant outer dimension.
19. A finger follower assembly for variably activating a valve of an internal combustion engine, the finger follower assembly comprising:
- a follower body having a first end portion configured to couple to the engine, a second end portion configured to couple to the valve of the engine, and an aperture formed in the first end portion;
- a cam follower supported by the follower body; and
- a latching mechanism at least partially positioned in the aperture and operable to selectively engage and disengage the cam follower to provide a first valve lift capability and a second valve lift capability, wherein the latching mechanism includes an engagement surface, and wherein the cam follower includes an engagement surface configured to engage the engagement surface of the latching mechanism, and wherein at least one of the engagement surfaces is at least partially convex.
20. The finger follower assembly of claim 19, wherein the engagement surface of the cam follower is at least partially convex.
21. A finger follower assembly for variably activating a valve of an internal combustion engine, the finger follower assembly comprising:
- a follower body having a first end portion configured to couple to the engine, a second end portion configured to couple to the valve of the engine;
- a cam follower supported by the follower body;
- a latching mechanism operable to selectively engage and disengage the cam follower to provide a first valve lift capability and a second valve lift capability, the latching mechanism at least partially defining a fluid chamber; and
- a vent passageway formed in the first end portion of the follower body and providing selective fluid communication between the fluid chamber and an outer surface of the follower body.
22. The finger follower assembly of claim 21, further comprising a movable member positioned at least partially within the vent passageway to provide selective fluid communication between the fluid chamber and the outer surface of the follower body.
23. The finger follower assembly of claim 22, wherein the fluid chamber communicates with a source of pressurized fluid, and wherein the movable member is movable in response to variations in a pressure of the source of pressurized fluid.
24. The finger follower assembly of claim 23, wherein the movable member is a piston positioned within a secondary passageway, the secondary passageway in fluid communication with the vent passageway.
25. The finger follower assembly of claim 24, wherein the secondary passageway is in fluid communication with the source pressurized fluid.
26. The finger follower assembly of claim 21, further comprising a second vent passageway that provides generally constant fluid communication between the fluid chamber and an outer surface of the follower body.
Type: Application
Filed: Sep 18, 2006
Publication Date: Oct 9, 2008
Applicant: TIMKEN US CORPORATION (Torrington, CT)
Inventors: Matthew J. Deierlein (Middlebury, CT), Brian Laird (Granby, CT), Richard F. Murphy (Torrington, CT)
Application Number: 12/065,954