Switchable cam follower

Details Switchable cam follower Switchable cam follower

1999-12-14

2001-07-10

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090500, C123S090550, C123S19800E

Reexamination Certificate

active

06257185

ABSTRACT:

FIELD OF THE INVENTION
The invention concerns a switchable cam follower for a valve train of an internal combustion engine, which valve train can be actuated indirectly by tappet push rods, said cam follower having the following features:
the cam follower can be installed in driving relationship between a camshaft and an end of the tappet push rod, said cam follower comprising an outer and an inner section as well as coupling means,
the outer section can be inserted with its outer peripheral surface into a reception of the internal combustion engine, the inner section being mounted in a recess of the outer section while being movable relative to the outer section,
one of said sections has a support for the end of the tappet push rod and the other of said sections has an axially opposite contacting surface for a cam of the camshaft,
said sections can be coupled to each other by the coupling means so that on coupling, a high lift of a valve train gas exchange valve loadable by the tappet push rod can be effected and, on uncoupling of the sections by the coupling means, a low lift or a zero lift of the gas exchange valve is obtainable.
BACKGROUND OF THE INVENTION
A cam follower of the pre-cited type known from U.S. Pat. No. 5,361,733 is considered to be of the generic type. This cam follower likewise comprises an outer and an inner section. However, the outer section is configured to be contacted by high lift cams and the inner section, by a low lift cam. Due to this configuration, the cam follower has a relatively large mass which has a negative effect on the oscillating masses in the valve train even in the uncoupled state. At the same time, the cam follower has a large overall width. Moreover, a set of three cams is required for each cam follower. This, in turn, unnecessarily increases the costs of valve actuation on the whole.
OBJECT OF THE INVENTION
It is therefore the object of the invention to create a switchable cam follower of the type described above in which the mentioned drawbacks are eliminated.
SUMMARY OF THE INVENTION
The invention achieves this object by the fact that
the outer section comprises the support for the end of the tappet push rod, and the inner section comprises the contacting surface for the cam of the camshaft,
the recess for the inner section in the outer section is made pot-shaped, the inner section, at its end remote from the contacting surface in the reception, is provided with an axle which is parallel to the axis of the camshaft and is guided in the outer section, the inner section being mounted on the axle for pivoting relative to the outer section,
the inner section is loaded by a spring means against its direction of pivot, and
the outer section is made so that it can be guided non-rotatably relative to its reception in the engine block.
By these measures, a switchable cam follower is created whose switching-off member (inner section), in contrast to the state of the art, is not caused by cam lift to move axially relative to the other tappet part (outer section) but pivots relative thereto. This has the advantage over switchable cam followers known from the state of the art that the proposed cam follower has a relatively small overall axial dimension or approximately the same dimensions as an unswitchable cam follower of the prior art. In particular, no design space is required any more in the outer tappet for the hitherto used compression spring.
Preferably, the proposed cam follower is intended to serve for a complete switching-off of the associated gas exchange valve. At the same time, it should be noted that only one cam is required per cam follower and that, advantageously, prior art camshafts can be used if the ramps of the cams are simultaneously raised.
By reason of the construction proposed by the invention, the cam follower possesses only a small oscillating mass in its switched-off state, and this oscillating mass is only minimally increased compared to hitherto known cam followers in the switched-on state. It must also be noted that the overall dimension of the cam follower in radial direction is relatively small.
According to a further proposition of the invention, the axle for the pivotable inner section is configured at the same time as a torsion spring. This reduces the number of components and simultaneously guarantees the relatively compact structure of the cam follower.
Although the invention proposes configuring the coupling means as slides, it is equally possible to use means such as pins, balls and coupling means indirectly actuated through wedge surfaces, and other similar means. Advantageously, the slides are configured as pistons, with their receptions being made as bores.
According to a further feature of the invention, the slides can be displaced in at least one of their directions of displacement by a servo means such as a hydraulic medium. This can be routed, for example, to an outer end face of the slide in question which, in the uncoupled state is situated in the inner section and is biased outwards in opposition to hydraulic medium pressure by the force of at least one compression spring means. However, it is also conceivable to arrange only one slide in the inner section and load this slide in its uncoupling direction by the force of the compression spring means and displace it in its coupling direction by a servo means.
According to a further proposition of the invention, the reception in the outer section extends therethrough and is made, for example, by drilling. This is particularly favorable from the manufacturing point of view. Bushings or stops can be inserted into these receptions to form, on the one hand, displacement limiters for the slides in outward direction, and on the other hand, they can be configured as stops for a rotation of the inner section relative to the outer section. The last-mentioned measures enable a simple positional co-orientation of the receptions of the sections for a displacement of the coupling means in the base circle phase of the respective cam. Thus, for example, a bushing can comprise a radially inwards pointing projection which cooperates with a corresponding track on the outer peripheral surface of the inner section.
According to another feature of the invention, a particularly low-friction cam follower is obtained by the fact that the contacting surface for the cam is configured as a roller preferably supported on a rolling bearing. However, it is also conceivable to use a friction bearing or an intrinsically frictional contact for the cam.
Advantageously, the cam follower comprises a hydraulic clearance compensation means. This dispenses with complicated mechanical clearance adjusting measures. The clearance compensation means is advantageously configured as an integral part of the support for the tappet push rod and arranged in a bore of the outer section.


REFERENCES:
patent: 5398648 (1995-03-01), Spath et al.
patent: 5402756 (1995-04-01), Bohme et al.
patent: 5669342 (1997-09-01), Speil
patent: 5934232 (1999-08-01), Greene et al.
patent: 5960756 (1999-10-01), Miyachi et al.

Affiliated with

Also associated with

Rating

Switchable cam follower does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Switchable cam follower, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switchable cam follower will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2442571