Switchable cam follower

Details Switchable cam follower Switchable cam follower

2000-03-31

2001-06-19

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090500, C123S090550

Reexamination Certificate

active

06247433

ABSTRACT:

FIELD OF THE INVENTION
The invention concerns a switchable cam follower of a valve train of an internal combustion engine, wherein
the cam follower comprises a housing adapted to be mounted with an outer wall in a bore of the internal combustion engine or in a bore of a component connected to the internal combustion engine,
the housing comprises a recess which encloses an inner element that is axially displaceable relative to the housing, each of said housing and said inner element comprising a reception extending in radial or secant direction, said receptions being aligned to each other in a defined relative position,
at least one coupling means is arranged in at least one of the receptions and said coupling means can be displaced toward the other of the receptions for coupling the inner element to the housing in said relative position,
a stop means extends between the housing and the inner element and prevents a rotation of the inner element relative to the housing while also forming an upper end stop for defining the relative position.
BACKGROUND OF THE INVENTION
A support element having a structure similar to the pre-cited cam follower is known from DE-A 197 10 578. The stop means of this support element comprises a narrow cylindrical element which extends in a recess of the housing and projects slightly in radially inward direction. In its inner region, this cylindrical element cooperates on the one hand with a longitudinal groove on the outer wall of the inner element and, on the other hand, with a bore-proximate shoulder of this longitudinal groove which acts as an upper end stop to define the relative position of the inner element and the housing.
A drawback of this prior art support element is that only an extremely short length of its stop means is fixed in the reception of the housing. At the same time, its extension toward the inner element by which the upper end stop and the prevention of rotation are realized has only a minimal dimension. This results in the formation of enormous stresses in the regions of fixation and of the upper end stop of the stop means when this is subjected to rotational and impact loads. Another danger is that the stop means may come loose from its locked position so that, in the worst case, an alignment of the receptions for the coupling means in the inner element and the housing for realizing the relative position is rendered more difficult or even impossible and, due to material loading, the surrounding material in the region of the stop means is deformed.
OBJECTS OF THE INVENTION
It is an object of the invention to create an improved switchable 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 a locking element such as a piston is arranged as a first component of the stop means in the reception of the inner element, an inner jacket section of the locking element extends over at least a substantial part of half a length of the reception, an outer jacket section of the locking element forming a second component of the locking element engages into a slot of the housing, the slot fixes the locking element in peripheral direction of the housing and has an axial dimension corresponding to at least a length of a desired relative displacement, one end of the slot forming the upper end stop, and the outer jacket section of the locking element extends at least through a largest possible dimension of the slot toward an outer peripheral surface of the housing.
Thus, by simple means, a switchable cam follower is created whose stop means is reliably fixed and in which the loading of components in the region of the stop means is greatly reduced. The use of the inventive measures in a cam follower not only drastically prolongs the useful life thereof but it also improves the reliability and quality of operation. This is particularly due to the fact that the fixing and stop length for the stop means is greatly increased over the prior art. The stress occurring in the region of the slot when the stop means abuts against the upper end stop in the region of one end of the slot is greatly reduced. A cam follower incorporating the measures of the invention is simpler as well as cheaper to manufacture than prior art devices. An additional advantage is that the slot leads to a noticeable reduction of the total mass of the cam follower and this has a positive influence on the oscillating masses of a valve train having a switchable cam follower in which the inventive measures are incorporated.
It is understood that the features of the invention can likewise be implemented in a support element of a lever-type cam follower so that the aforesaid advantages can also be attained with such a support element.
According to a further feature of the invention, the coupling means is configured as a piston and arranged in the reception of the inner element diametrically opposite the locking element. This measure leads to a reduction of the number of components required compared to the cited prior art because the locking element serves at the same time as a support for one end of the spring in the reception of the inner element. A person skilled in the art will also recognize that the snap ring of the mentioned prior art can be omitted because, according to a further proposition of the invention, the reception for the coupling means in the housing has a stepped configuration and forms a stop for the coupling means. However, other stop measures such as separate stop elements or lugs and the like projecting into the bore are also conceivable.
According to an advantageous feature of the invention, a displacement of the coupling means in its uncoupling direction is achieved by a hydraulic medium which can be conducted in a simple manner to an outer end face of the coupling means through the reception of the housing. For this purpose, in the installed state, the reception of the housing communicates with an appropriate passage in the internal combustion engine. The coupling means may also be displaced in both directions of displacement by the hydraulic medium, or the described kinematic principle may be reversed.
Advantageously, a hydraulic clearance compensation element is installed in the inner element. This adjusts in a manner, known, per-se, during a base circle phase of the actuating cam, the entire play occurring in the valve train to zero.
According to a further feature of the invention, the cam follower is configured as a roller tappet which cooperates directly with a bottom camshaft and acts at its camshaft-distal end on a push rod. However, the invention is also applicable to a cam follower configured as a switchable cup tappet as well as to cam followers or support elements in which the coupling means is arranged in the housing and displaced toward the inner element to establish the coupled state.
According to a final proposition of the invention, an anti-rotation device configured as an extension or a pin is fixed in the outer wall of the housing and extends beyond this outer wall. The housing, and thus also the cam follower, is positionally fixed by this anti-rotation device relative to the bore of the internal combustion engine. The anti-rotation device may be a simple cylindrical body or a ball, but may also be made integrally with the housing, for example, as a tab.


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