Patent Application
20100236507
The invention relates to a switchable cam follower of a valve train of an internal combustion engine, with an external lever which is encompassing an internal lever between its arms, which levers are pivotably moveable relative to one another on an axis that is applied to a valve-side end, wherein the cam follower has a stop for a gas-exchange valve on an underside on the valve-side end and on the other end has a complementary face for a support element, wherein the cam follower has a start face on an upper side for at least one high-lift cam, wherein in a receptacle of one of the cams a coupling means is seated, which can be brought into engagement in sections in case of coupling (high-lift) with a driving surface of the respective other lever and wherein at least one torsion spring is clamped between the two levers as lost motion spring.
A cam follower of this kind, in this case embodied as a lift deactivation means, is already known from U.S. Pat. No. 5,544,626. The torsion springs of which extend on the valve-side end of the cam follower. As a result of the application of the torsion spring on the one end, a relatively high mass moment of inertia is present. Also, unnecessary installation space is utilized which is essentially outside of the geometry of the cam follower.
Further switchable cam followers with torsion spring on the valve-side end emerge from, for example, DE 103 45 307 A1 and DE 10 2006 023 772 A1.
Although the at least one start face for the cam could, in the embodiments according to the state of the art mentioned above, be displaced further in the direction of the support element, in order to provide a contribution for the lowering of the mass moment of inertia. On the other hand, at the same time, the leverage forces would be drastically increased when the cam is activated. Therefore, a “central” position of the respective start face presents a good compromise.
It is therefore the object of the invention, to develop a switchable cam follower of the kind mentioned above, in which the mentioned disadvantages are eliminated. In particular, a cam follower is to be developed, whose mass moment of inertia is reduced in a design that is simple at the same time.
According to the invention, this object is achieved in that the respective torsion spring is seated on an axle journal, which extends in a region of a longitudinal section of the cam follower situated in the immediate vicinity of the complementary face.
Consequently, a switchable cam follower is available, in which the disadvantages mentioned in the outset are eliminated. The mass of the at least one torsion spring no longer affects the mass moment of inertia of the cam follower so as to increase it unnecessarily.
According to a particularly preferred embodiment, exactly two axle journals are provided, which protrude, for example, from an outer side wall of the internal lever or above the complementary face. Every axle journal is encompassed by a torsion spring or a torsion spring packet. Alternatively, a “continuous” axle is conceivable and provided.
In an implementation of the invention, it is proposed to form the respective axle journal either as a separate component or so that it protrudes in one piece from the corresponding side wall (outer side wall of the internal lever/inner side wall of the external lever). A multi-part design is expedient, for example, if the corresponding lever element is manufactured from a lightweight construction material such as sheet steel. If the lever element is to be formed in a casting process or the like, the respective axle journal may be an integral part of the corresponding side wall.
Likewise it is advantageous to design the external lever in a box-like fashion, so that its side walls encompass the axle journals from the side, and in the region of the other end, in front of the rear end of the internal lever, merges into a bracket. The preferably two torsion springs therefore proceed inside of the extension of the cam follower. At the same time, a particularly rigid external lever is present, which may be minimized with respect to its mass.
Further subclaims refer to expedient forms of abutment of the limbs of the respective torsion spring. According to one variation, a first limb of the torsion spring is to extend in a recess of the bracket of the external lever on the other side, whereas according to a further variation, the first limb of the torsion spring engages under the start face on the external lever, which start face is embodied as a wing-like pad. For the abutment of the other limb of the torsion spring, it is provided that a one-piece or multi-part shoulder or the like is protruding from the inner sidewall of the internal lever, against which the other limb is acting.
The pad mentioned above acting as a start face on the external lever may extend from its upper side in the shape of a wing, or point to the inside in the direction of a longitudinal center plane of the cam follower. Preferably, this pad (per arm of the external lever) should be an integral part of the external lever and be appropriately provided, for wear protection, with applied layers and/or measures for heat treatment.
According to a further implementation of the invention, the cam follower is designed as a so-called “lift switch”. The external lever of said lift switch, for example, has two pads (sliding surfaces) as stop faces for the cam for associated high-lift cams, whereas for a stop face for the low-lift cam, a rotatable roller mounted on a bearing is provided in the internal lever. If appropriate, in both cases pads or rollers may be provided or the internal lever may have a pad and the external lever have rollers. The extent of protection of the invention, however, also refers to a cam follower which functions as a so-called “lift deactivation means”.
A further sub-claim refers to a functional embodiment and arrangement of the coupling means. Accordingly, said coupling means is to be formed as a slider, which is seated in the internal lever preferably above the complementary face which is embodied as a spherical cap and which coupling means is, in the case of coupling, engageable with a driving surface of an end-side bracket of the external lever. The arrangement of the coupling means in the region of the spherical cap and, therefore, of the pivot center of the cam follower is a further contribution to the lowering of the mass moment of inertia. The coupling means may be, for example, a piston, whose engaging section may be cylindrical or flattened.
It is further provided in a development of the invention, to provide a stop for the external lever on the internal lever, so that, for instance, a flush position of the receptacle for the coupling means with respect to the driving surface or, at least, a simple rotation stop is given. An attachment, which is projecting from an upper end side of the internal lever, is provided for the stop, the underside of which attachment communicating with an upper side of the bracket on the end side of the external lever, in the case of engagement.
Although a spherical cap-shaped molding on the underside of the internal lever is particularly expedient as a complementary surface for the support element, it is also conceivable and provided to apply a joint or the like in this area. At this point, it is appropriate to feed hydraulic fluid for the “actuation” of the coupling means from the support element via the spherical cap-like molding in at least one displacement direction.
The invention is expediently explained by means of the drawing, in which:
A switchable cam follower 1 in box construction is shown. The cam follower 1 comprises an elongate external lever 2, which encloses between its arms 3 an internal lever 4 pivotably movable relative to it. Both levers 2, 4 are mounted in the region of a valve-side end 5 on a mutual axis 6.
The internal lever 4 has on its underside 7 at the valve-side end 5 a stop 8 for a gas-exchange valve. On the other end 9, the internal lever 4 has a complementary face 10 embodied as spherical cap here, for mounting on a head of a hydraulic support element. Approximately in the region of a longitudinal center, the arms 3 of the external lever 2 have a start face 12 (sliding surface) embodied as a pad for associated high lift cams. The internal lever, in turn, which is also formed from two enlongate arms, has a roller mounted on a roller bearing or a plain bearing as a start face 32 for a low-lift cam.
The internal lever 4 has a receptacle 13 extending in the longitudinal direction above the complementary face 10 for a piston serving as coupling means 14. The latter is displaceable in sections in case of coupling under a driving surface 15 of a bracket 21 which connects the arms 3 of the external lever 2 at the other end 9. In case of coupling, lift of the high-lift cam is transmitted, as is known to a person skilled in the art, which cam is contacting the arms 3 of the external lever 2, wherein in case of decoupling, only the internal lever 4 is active and the gas exchange valve opens in terms of the low-lift cam contacting the internal lever 4.
Two torsion springs are provided as lost-motion spring means 16. For the mounting of which torsion springs one axle journal 17 per outer side wall 18 of the internal lever 4 is protruding in the longitudinal section region of the complimentary face 10. The axle journal 17 may be a one-part or multi-part component of the respective outer side wall 18. Outer ends of the axle joints 17 are covered by the arms 3 of the external lever 2. Therefore, the torsion springs 16 extend inside the extension of the cam follower 1.
According to the embodiment in
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Because of the arrangement of the torsion springs 16 in the immediate region of a pivot center of the cam follower 1, the cam follower has only a relatively low mass moment of inertia.
This application claims the priority of U.S. Provisional Application No. 61/161,679, filed Mar. 19, 2009 and incorporates the same by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61161679 | Mar 2009 | US |
