COUPLING MECHANISM

MECANISME D'ACCOUPLEMENT

English Abstract

The invention proposes a coupling mechanism (1) for relatively movable
elements
(2, 3) of a switchable cam follower (4) of a valve train of an internal
combustion
engine, a high lift being obtainable upon coupling of said elements (2, 3) and
a lift
smaller than the high lift being obtainable upon uncoupling of said elements
(2, 3),
a first one (2) of said elements comprising a guide bore (5) for at least one
coupling piston (6) which, for achieving coupling, can be displaced partly
beyond a
parting surface (7) between said elements (2, 3) into an aligned reception (8)
of a
second one (3) of said elements, wherein upon cam lift and coupling of said
elements (2, 3), a contact zone (9) between the piston (6) and the reception
(8) is
clearly spaced from an edge section (10) of the reception (8) on the parting
surface (7). This can be implemented in practice, for instance, through a
special
"backwards" oriented flattened portion (14) on the piston (6). Material
loading on
the edge section (10) is thus avoided.

Claims

7
Claims
1. A coupling mechanism for relatively movable elements, typically for a
switchable cam follower, a switchable cam follower group or a switchable
support device of a valve train of an internal combustion engine, a high lift
being obtainable upon coupling of said elements and a lift smaller than the
high lift being obtainable upon uncoupling of said elements. a first one of
said
elements comprising a guide bore for at least one coupling piston which, for
achieving coupling, can be displaced partly beyond a parting surface
between said elements into an aligned reception of a second one of said
elements, wherein, upon cam lift and coupling of the elements, a contact
zone between the piston and the reception is clearly spaced from an edge
section of the reception on the parting surface.
2. A coupling mechanism of claim 1, wherein the contact zone of the piston is
determined by an axially outer edge region of the piston on an outer end face
of the piston as viewed in coupling direction.
3. A coupling mechanism of claim 2, wherein, starting from the contact zone,
the piston tapers relative to a perpendicular line of the parting surface at
least
in this peripheral section or on this side toward an inner end face
4. A coupling mechanism of claim 2, wherein starting from the edge section on
the parting surface, the reception tapers relative to a perpendicular line of
the
parting surface at least in this peripheral section or on this side at least
up to
the contact zone.
5. A coupling mechanism of claim 2 wherein, starting from the contact zone,
the
piston tapers relative to a perpendicular line of the parting surface at least
in
this peripheral section or on this side toward an inner end face and wherein,

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starting from the edge section on the parting surface, the reception tapers
relative to a perpendicular line of the parting surface at least in this
peripheral
section or on this side at least up to the contact zone.
6. A coupling mechanism of claim 3, wherein an angle a of taper relative to
the
perpendicular line of the parting surface is situated in a range of 0°
< .alpha. .ltoreq. 5°.
7. A coupling mechanism of claim 4, wherein an angle a of taper relative to
the
perpendicular line of the parting surface is situated in a range of 0°
< .alpha. .ltoreq. 5°.
8. A coupling mechanism of claim 5, wherein an angle a of taper relative to
the
perpendicular line of the parting surface is situated in a range of 0°
< .alpha. .ltoreq. 5°.
9. A coupling mechanism of claim 3, wherein an angle a of taper relative to
the
perpendicular line of the parting surface is situated in a range of 5' <
.alpha. .ltoreq. 5°.
10. A coupling mechanism of claim 4, wherein an angle a of taper relative to
the
perpendicular line of the parting surface is situated in a range of 5' <
.alpha. .ltoreq. 5°.
11. A coupling mechanism of claim 5, wherein an angle a of taper relative to
the
perpendicular line of the parting surface is situated in a range of 5' <
.alpha. .ltoreq. 5°.
12. A coupling mechanism of claim 3, wherein, at least in a region between the
edge section and the contact zone, the reception is made as a bore.
13. A coupling mechanism of claim 4, wherein, at least in a region between the
edge section and the contact zone, the reception is made as a bore.
14. A coupling mechanism of claim 3 wherein, at least a region between the
edge section and the contact zone, the reception has a flat configuration.

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15. A coupling mechanism of claim 4 wherein, at least a region between the
edge section and the contact zone, the reception has a flat configuration.
16. A coupling mechanism of claim 3, wherein a taper of the piston is
configured
as a continuous cone or has a cone-like configuration.
17. A coupling mechanism of claim 3, wherein a taper of the piston is made as
a
flattened portion.
18. A coupling mechanism of claim 17, wherein a peripheral section of the
piston
outside of the flattened portion is cylindric.
19. A coupling mechanism of claim 1, wherein a stop element for the piston is
arranged in the reception.

Description

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Coupling mechanism
Field of the invention
The invention concerns a coupling mechanism for relatively movable elements,
typically for a switchable cam follower, a switchable cam follower group or a
switchable support device of a valve train of an internal combustion engine, a
high
lift being obtainable upon coupling of said elements and a lift smaller than
the high
lift being obtainable upon uncoupling of said elements, a first one of said
elements
comprising a guide bore for at least one coupling piston which, for achieving
coupling, can be displaced partly beyond a parting surface between said
elements
into an aligned reception of a second one of said elements.
Background of the invention
A coupling mechanism of the pre-cited type considered as generic is disclosed
in
US 2002/0046718 A1. The play of the piston required in the reception of the
outer
element for achieving coupling, causes the piston to tilt in the reception.
This
always occurs during cam lift because an undersurface of the piston abuts
against
a corresponding counter surface of the reception of the outer element. Due to
the
tilting of the piston, a contact zone is displaced from the interior of the
reception to
an edge section of this toward the parting surface between the elements. If
the
reception into which the piston engages is a bore, only a point contact is
made. In
the case of a flattened piston that is displaced, for example, into a
reception in the
form of an annular groove in the outer element, a two-point contact is
determinable.
The aforesaid point contact in the edge section leads to an extreme
augmentation
of the contact forces. If, additionally, undesired large deviations of form,

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rectangularity and parallelism exist, the aforesaid effect is aggravated. Due
to the
extremely high loads acting precisely on the edge section, the play in the
coupling
region increases in an unfavorable manner over the operating lifetime of the
cam
follower. This leads to a deformation of the edge section which, in the worst
case,
can result in binding between the two elements.
Objects of the invention
It is an object of the invention to provide a cam follower of the pre-cited
type in
which the aforesaid drawbacks are eliminated.
This and other objects and advantages of the invention will become obvious
from
the following detailed description.
Summary of the invention
The invention achieves the above objects by the fact that, upon cam lift and
coupling of the elements, a contact zone between the piston and the reception
is
clearly spaced from an edge section of the reception on the parting surface,
so
that the contact zone is shifted inward into the reception. Contact between
the
piston and the reception is established preferably in an edge region of the
piston at
an outer end face of the piston.
The drawbacks described above are effectively avoided with the aforesaid
measures. During the unavoidable tilting of the piston in its reception in
case of
coupling, the contact zone of the invention is displaced structurally away
from the
endangered edge section.
Although the invention is directed particularly to coupling mechanisms in cam
followers, cam follower groups and switchable support devices for cam
followers
or cam follower groups, the scope of the invention is clearly much broader. In
general, the inventive means can also be implemented in camshaft adjusting

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devices, for example in locking arrangements of such devices, in engine brake
systems or even in pump drives.
A simple measure for shifting the contact zone into the interior of the
reception
upon coupling consists in modifying the piston itself. If, for instance, as
disclosed
in the cited prior art US 2002/0046718 A1, the piston has a stepped
configuration
and engages for achieving coupling into an annular groove of the outer
element,
the flattened portion of the piston serving as a coupling surface would be
configured in the case of the present invention so as to taper toward an inner
end
face of the piston. In the region of the flattened portion, this piston, when
viewed in
longitudinal section, would thus have a quasi backward oriented conical or
wedge-
like shape.
Alternatively, the invention also proposes to configure the piston without a
flattened portion but to make its taper as a circumferential, backward
oriented
cone or cone-like structure.
According to a further proposition of the invention, the outer periphery of
the piston
is entirely cylindric but the complementary reception in the outer element
tapers in
coupling direction at least in the coupling region.
If necessary, the contact zone can also be shifted inwards by providing a
combined inclination on appropriate contact surfaces of the piston and the
reception.
According to a further feature of the invention, the angle of taper a is
situated in
the range of 0° < a <_ 5°, a particularly preferred range lying
between 5' and 5°. If
necessary, even this specified value of 5° may be slightly or strongly
exceeded.
All in all, the invention offers a great number of possible geometric
combinations
between the piston and the reception.

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According to a further proposition of the invention, a stop for the coupling
element
is arranged in the reception. This stop determines an end position of the
piston in
case of coupling, and, if the reception is made in the form of a through-hole,
the
piston cannot extend unintentionally out of this reception of the outer
element.
The invention will now be described more closely with reference to the
appended
drawing.
Brief description of the drawing
Fig. 1 shows a switchable cam follower in a longitudinal section.
Fig. 2 illustrates a coupling mechanism comprising a cylindrical piston, in
coupled state,
Fig. 3 illustrates a coupling mechanism comprising a flattened piston, in
coupled state, and
Fig. 4 shows the piston of Fig. 3 comprising the features of the invention.
Detailed description of the drawing
Fig. 1 shows a longitudinal section through a switchable cam follower 4. This
is
configured in the present case as a roller tappet and comprises an outer
element 3
that is inter-inserted with an inner element 2. The outer element 3 comprises
a
contact surface for a cam on one end, while the inner element 2 acts at an
opposite end on a tappet push rod in lift direction of the cam.
Further, a coupling mechanism 1 of a type known, per se, is integrated in the
cam
follower 4. This coupling mechanism 1 comprises a guide bore 5 that extends
radially through the inner element 2, and a reception 8 in the outer element
3,
which reception is aligned to the guide bore 5 in case of coupling. Further, a

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coupling element in the form of a piston 6 extends in the guide bore 5. For
achieving coupling, this piston 6 can be displaced radially outwards, by means
needing no further specification, partly beyond a parting surface 7 between
the
elements 2, 3 into the reception 8. If desired, a stop element 15 may be
arranged
in the reception 8 for limiting the piston travel.
As discussed more clearly above and as best shown in Figs. 2 and 3, the
reception 8 has a play relative to the piston 6. Due to this play, the
interlocking
established upon coupling manifests a relatively low osculation factor.
Therefore,
the piston 6 compulsorily tilts in the reception 8 and in the guide bore 5
during cam
lift. In the case of a completely cylindrical piston 6 as represented in Fig.
2, this
results in a high-loading point contact of the piston 6 with the lower edge
section
of the reception 8 at the parting surface 7. Due to the resulting wear, the
play in
the region of coupling increases. In undesired manner, the edge section 10 is
gradually deformed and, given the conditions, a binding of the elements 2 and
3
can occur.
The same applies to the embodiment of Fig. 3 in which the piston 6 comprises a
flattened portion 14 on the underside that in case of coupling extends onto a
flat
counter surface of a continuous annular groove constituting the reception 8 of
the
outer element 3. In case of tilting, a two-point contact with the reception 8
is to be
expected.
Fig. 4 shows an advantageous embodiment of the invention in which a contact
zone 9 between the piston 6 and its counter surface in the reception 8 is
shifted
inwards (as viewed in coupling direction) away from the edge section 10.
Accordingly, this contact zone 9 is situated inside the reception 8 and, when
coupling is completed, it lies directly in the edge region 11 of the piston 6
at its
outer end face 12. On the side of the contact zone 9, the piston 6 comprises a
flattened portion 14 which is situated opposite a flattened counter surface of
the
reception 8 that is configured in the form of an annular groove. With
reference to a
perpendicular line of the piston 6 to the parting surface 7, the flattened
portion 14

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is inclined in a quasi backward direction. The angle a of this inclination is
situated
in the range of 0° < a s 5°, and may preferably start from 5'.
It goes without saying that this backward oriented inclination may also be
circumferentially configured so that a backward oriented cone is generated
that
then extends, for example, into a complementary reception 8. As disclosed in
Fig.
4, in case of coupling, the flattened portion 14 results in the formation of a
line
contact in the contact zone 9 in contrast to the disadvantageous two-point
contact
of the prior art.

Representative Drawing