Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2000-09-05
2001-08-14
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090500, C123S19800E
Reexamination Certificate
active
06273041
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a cam follower in a valve train of an internal combustion engine switchable between different lifts for at least one gas-exchange valve and having the following characteristics:
a) the cam follower includes at least two adjoining sections acted upon by cams with different lift, one of these sections alternatively not cooperating with a cam;
b) the sections possess cavities preferably aligned with each other in a cam base-circle phase, movable coupling means in at least one of the cavities, the means being positioned in the decoupled state of the sections completely in their cavity;
c) the coupling means can be shifted in the coupling direction via hydraulic fluid which can be delivered via an inlet to a pressure chamber formed by their cavity axially in front of their end wall on the pressure-chamber side, the means being shiftable across a separating surface between the sections for coupling of the sections such that part of the means engages in the adjoining cavity;
d) the coupling means communicate with locking or shut-off means.
A cam follower of this type with locking means is known from DE-OS 196 22 174. According to FIG. 8, for example, its locking means have the form of a ball which is designed to engage in positive fashion into the piston-shaped coupling means. Here, the ball extends beyond a cavity for the coupling means in the direction of the cam shaft. An engaging cam, in turn, possesses on its outer wall a partially recessed annular groove which cooperates with the ball for locking purposes.
A disadvantage of this type of cam follower is the fact that the locking means require complicated changes to already existing cams of cam shafts. At the same time, unnecessarily high wear occurs in this region of the locking means through the cam contact. If hydraulic fluid is introduced ahead of the coupling means possessing the locking means, one also has to reckon with an additional loss of hydraulic fluid via the recess in the cam follower for the locking means. One likewise finds that the measures undertaken on the mentioned cam follower for locking its coupling means outside the desired cam-contact phases themselves necessitate complicated changes in the cam follower. At the same time, the stiffness of the locking means can lead in rare cases to undesired loading or destruction of structural parts.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide a cam follower of the type described above in which the mentioned disadvantages are eliminated.
The locking means are produced according to the present invention as a mechanically closable and openable shut-off slide for the inlet to the pressure chamber (the slide, however, being maintainable hydraulically in its open position via high switching pressure) and/or the shut-off means are completely incorporated in the cam follower and do not extend beyond it.
This inventive shutting off and opening is realized in the embodiment of the present invention via a signal track on the outer shell of one of the sections. As a result, the difficult-to-produce signal tracks on the opposing cam can be foregone. The wear otherwise found in this area is eliminated. However, also conceivable here is positioning the signal track in the area of a structure surrounding the cam follower (e.g., the cylinder head).
As a result of the fact that the shut-off means are maintained hydraulically in their open position only with high switching pressure, they close the inlet for hydraulic fluid to the pressure chamber ahead of the coupling means when there is insufficient hydraulic fluid pressure. Thus, using the signal track in the disengaged state of the sections and advantageously at their maximum relative lift, the inlet is checked for sufficiently high hydraulic fluid pressure. If this is sufficient, then the slide, after being opened by the signal track, is held or shifted by the applied hydraulic fluid pressure such that it frees a sufficient cross-section at the inlet for displacement of the coupling means. In the following base circle phase, the consequently hydraulically pretensioned coupling means are shifted with extremely high certainty and speed into their opposing cavity for coupling of the sections (see also figure description).
In appropriately developing the present invention further, it is proposed that the cam follower be designed as a cup-shaped tappet. The range of protection of the present invention relates, however, to any other type of cam follower, especially lever-like cam followers such as rocker-arm or finger-lever pairs. Also conceivable are cam followers in which three or more levers are positioned next to each other and can be joined by coupling means for purposes of different lift. Naturally, the means for coupling these levers can then likewise be provided with the inventive shut-off means.
The end wall of the coupling means facing the pressure chamber communicates according to the present invention only sectionally with the end wall of the shut-off means facing the pressure chamber so that the hydraulic fluid can be delivered with sufficient speed to the pressure chamber formed between these end walls upon shifting of this packet by the signal track.
As elastic means for loading the shut-off means, a compression spring is proposed, for example. However, any other spring means are conceivable here, including magnetic or even hydraulic loading of the shut-off means in the direction of the pressure chamber.
In an appropriate embodiment of the present invention, the tappet exhibits a hydraulic lash-adjusting element in the area of its circular section. This is advantageously loaded by hydraulic fluid pressure via a separate hydraulic fluid path.
In order to minimize surface pressure in the case of coupling of the sections by the coupling means and in order to provide means for expelling the coupling means in the decoupling direction, it is proposed according to the present invention to apply in the circular section a slide extending over the entire length of this section's cavity. In case of coupling of the sections, this slide engages in a cavity in the annular section lying diametrally opposite the cavity for the coupling means. As a result of this “symmetric” coupling, even a minimal skewing of the sections with respect to each other during coupling is simultaneously avoided. The annular section is advantageously loaded in the area of its base by two cams with an equal and large lift. These cams enclose a cam with small lift for the circular section. If the acted-on gas-exchange valve is to remain completely closed in the decoupled state of the sections, one can forego the small-lift cam or have the small cam produce only a minimal lift.
In carrying out the present invention, it is proposed that the slide be provided with a compression spring. This spring, for example, can surround the slide. The compression spring loads the slide in the decoupling direction and causes displacement of the coupling means completely into their cavity for the case of desired decoupling upon decreasing hydraulic fluid pressure. Here, the force of this compression spring is designed to be stronger than the force of the compression spring loading the shut-off means. At the same time, this compression spring acting on the slide also plays a role in keeping coupling from being realized upon insufficiently high switching pressure of the hydraulic fluid. However, it is also conceivable to load the slide in the decoupling direction via hydraulic fluid. A further suitable form of loading would involve having an additional structural member, for example, another slide, operating in the cavity diametrally opposing the cavity for the shut-off means. This could act on the slide in the decoupling direction via the mentioned loading means (hydraulic, mechanical) and optionally also form or include a stop.
The cited spring means for the shut-off means are designed such that they permit displacement of the shut-off means in their opening direction via hydraul
Haas Michael
Karbstein Henning
Nitz Norbert
Ina Walzlager Schaeffler OHG
Lo Weilun
Volpe & Koenig PC
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