Patent Application
20070039575
The invention relates to a guide rail for guiding cylindrical valve tappets of an internal combustion engine. The guide rail is essentially comprised of a metallic material and has receptacle spaces, which are arranged at intervals over its longitudinal extent, which are each used for receiving one of the valve tappets, and in which there are flattened sections, which are spaced apart in parallel and which interact with a positive fit with key surfaces of the valve tappet, such that the valve tappet is secured against twisting about its longitudinal axis. Here, the flattened sections permit the valve tappet to be aligned orthogonal to its longitudinal axis and parallel to the flattened sections.
Such a guide rail is used for rotation protection of valve tappets, which are typically embodied as roller tappets of a push rod valve train. Simultaneously, they can be used as installation aids for the valve tappet, in that the guide rail and the valve tappets form one structural unit that is protected from loss during transport and installation, so that several valve tappets can be installed simultaneously into the tappet guides of the internal combustion engine.
From DE 101 63 411 A1, which is considered a class-forming invention, a sheet-metal guide rail emerges, which has an especially flat shape and therefore is superior in terms of overall height in comparison with guide rails made from plastic, which are also disclosed in this publication. Plastic guide rails can indeed be produced economically as one-piece injection-molded parts and are also exceptionally well suited, through their own deformation, for equalizing tolerance-related positional deviations in surfaces that are part of the tappet guide system due to their relatively low material stiffness. These surfaces include the tappet guides, the flattened sections of the guide rail, as well as the key surfaces of the valve tappet. Nevertheless, even this low material stiffness must be compensated by increased dimensional stiffness in the longitudinal direction of the valve tappet, so that the overall height of such guide rails can exceed the available installation space in modern internal combustion engines with compact constructions.
While the guide rail proposed in the cited publication, which is composed of sheet metal with a flat overall height, exhibits sufficient dimensional stiffness in the longitudinal direction of the valve tappet, disadvantageously it can also deform only slightly orthogonal to its longitudinal extent and to the longitudinal axis of the valve tappet. The cause here is essentially the relatively high material stiffness of the sheet metal in connection with the high geometrical moment of inertia of the guide rail in this direction. The flattened sections extending parallel to the longitudinal extent of this guide rail are indeed wider than the key surfaces of the valve tappet and therefore permit a free alignment of the valve tappet parallel to the flattened sections; however, compensation of tolerance-related positional deviations is made considerably more difficult due to the high dimensional resistance of the guide rail orthogonal to the flattened sections.
In addition, the flattened sections in the receptacle spaces for the valve tappets are embodied very low and are therefore exposed to a considerable risk of wear as metallic surfaces in their function as rotation protection for the valve tappet. Theoretically this risk of wear can be minimized by subjecting the guide rail to a heat treatment for surface hardening of the flattened sections, but this heat treatment can lead to an impermissibly high dimensional deformation of the guide rail. The alignment errors of the flattened sections with reference to the key surfaces of the valve tappet, in association with such dimensional deformation, can then in practice increase the wear susceptibility of the flattened section despite surface hardening, because the valve tappet mounted in the tappet guides become clamped under the application of considerable transverse forces on the key surfaces between the flattened sections due to the high dimensional stiffness of the guide rail. Simultaneously, it has proven to be extraordinarily difficult to keep this dimensional deformation within tolerable limits in the production of the guide rails in a reliable process, so that there is always the risk of an increased rejection rate and consequently higher costs per piece for the guide rail.
Therefore, the objective of the invention is to construct a guide rail of the type named above, so that the cited disadvantages are solved with simple means. Accordingly, the guide rail should guarantee rotational protection of the valve tappets over the service life of the internal combustion engine for the smallest possible overall height and here should simultaneously compensate for tolerance-related positional deviations, especially of the tappet guides relative to each other, as well as alignment errors of the flattened sections with reference to the key surfaces of the valve tappet installed in the tappet guides also in the orthogonal direction relative to the flattened sections and independent of the orientation of the flattened section relative to the longitudinal extent of the guide rail.
This object is met by the invention. Accordingly, the guide rail should enclose a metal carrier and rotational protection elements, which are fixed in recesses of the metal carrier, which have flattened sections, and which also permit alignment of the valve tappet orthogonal to its longitudinal axis and orthogonal to the flattened sections, in that the flattened sections each belonging to one of the receptacle spaces can be displaced individually or in common orthogonal to the flattened sections relative to the metal carrier.
In this way, the low requirements for installation space of metallic guide rails can be combined advantageously with the properties of plastic rails that compensate for tolerance-related positional deviations. By dividing the different functions of the guide rail to the metal carrier and the rotational protection elements, these components are separated and selectively optimized with reference to different requirements. Thus, on one side, tolerance related positional deviations both of the tappet guides and also of the receptacle spaces can be compensated despite the dimensionally stiff metal carrier, such that the flattened sections displaceable relative to the metal carrier are adapted to the corresponding position of the key surfaces of the valve tappet located in the tappet guide and these can be protected from torsion with low transverse force. On the other side, because the flattened sections are arranged on the rotational protection elements, simultaneously a heat treatment for the metal carrier for the purpose of protecting the flattened sections from wear can be eliminated in favor of a reliable processing production of the metal carrier and thus reduced production costs of the guide rail.
In another construction of the invention, the rotational protection elements should be dimensionally elastic. For free material selection for the rotational protection elements, in this way a holder for the valve tappet in the guide rail can also be realized for forming a structural unit that is protected from loss with simple means. In comparison with the positive-fit axial locking of the valve tappet in the guide rail proposed in the cited state of the art, for this purpose it is proposed that an inner spacing of the flattened sections is dimensioned so that these surround the key surfaces of the associated valve tappet without play. The resulting frictional surfaces between the flattened sections and the key surfaces of the valve tappet prevent, first, the valve tappet from falling out of the guide rail during transport and installation, so that a common insertion of several valve tappets into the tappet guides is enabled for simultaneous installation of the guide rail in the internal combustion engine. Second, the dimensionally elastic rotational protection elements permit a sufficiently exact controlling of these friction forces, such that the friction losses occurring during the operation of the internal combustion engine are at a negligible level.
The displaceability of the flattened sections can be simplified in a preferred improvement of the invention, such that an air gap is formed between the rear sides and the recesses of the metal carrier. Independent of the dimensional elasticity of the rotational protection elements, this air gap can be combined with a rotational protection element, which is mounted floating in the associated recess in the direction orthogonal to the flattened sections. Here, a rotational protection element can be allocated to each of the receptacle spaces. Such a rotational protection element preferably has a frame-like shape and sliding surfaces, which are mounted so that they can move longitudinally from guide surfaces in the recesses of the metal carrier. Here, the guide surfaces and the sliding surfaces extend orthogonal to the flattened sections.
In addition it is provided that the rotational protection elements are composed of glass fiber-reinforced plastic. This material has already been proven multiple times to be a more economical and wear-free contact partner for rotation protected valve tappets. Here, such rotational protection elements can be fixed on the metal carrier as injection-molded parts produced separately from the metal carrier by means of a clamping or snap-on connection. Alternatively, it is also conceivable that the rotational protection elements are injection molded onto the metal carrier in a plastic injection molding method. In the end, this should be produced economically as a stamped part.
Additional features of the invention emerge from the following description and from the drawings, in which the guide rail according to the invention is shown as an example with reference to variants of the rotational protection elements. Shown, each in perspective view, are:
In
However, a lifting movement of the valve tappet 2 with as little resistance as possible is to be achieved only by taking into account and compensating to the greatest extent unavoidable component tolerances, which can also lead to alignment errors of the flattened sections 6 in reference to the key surfaces 7 of the valve tappet 2 installed in the tappet guides. In the embodiment, because the flattened sections 6 extending parallel to the longitudinal extent of the guide rail 1 are wider than the key surfaces 7, each valve tappet 2 can be aligned parallel to the longitudinal extent of the guide rail 1 in the rail. The similarly necessary alignment of the valve tappet 2 transverse to the longitudinal extent of the guide rail 1 is enabled in this carrier despite the high dimensional stiffness of the metal carrier 3, such that the flattened sections 6 are formed not directly on the metal carrier 3, but instead on rotational protection elements 8, 9, so that the flattened sections 6 can be displaced relative to the metal carrier 3 transverse to the longitudinal extent of the guide rail 1.
As explained below, the rotational protection elements 8, 9 are formed differently and fixed on the metal carrier 3. In
In the first variant, the rotational protection elements 8 are injection molded on the metal carrier 3.
As an alternative to the injection-molded rotational protection elements 8, the rotational protection elements 9 are formed as injection-molded parts produced separately from the metal carrier 3 and fixed by means of a clamping connection on the metal carrier 3. One of the rotational protection elements 9 is shown, also greatly enlarged, in
Another variant of a guide rail 22 is shown in
Finally, as also provided in the previously described variants, the guide rail 22 forms one structural unit 29 that can be installed into the internal combustion engine in common with the valve tappets 2, with the receptacle spaces 4 being used both for guidance and also for holding the valve tappet 2 so that it cannot be lost during transport and installation of the structural unit 29.
For this purpose, an inner spacing 30 of the flattened sections 6 is dimensioned so that the key surfaces 7 of the valve tappet 2 engage without play, so that the resulting friction forces between the flattened sections 6 and the key surfaces 7 effectively prevent the valve tappet 2 from falling out of the guide rail 22. Depending on the material that is used for the rotational protection elements 23, it is useful to shape the inner spacing 30 of the flattened sections 6 for not yet installed valve tappets 2 somewhat smaller than an outer spacing 31 of the key surfaces 7 (
This application is a non-provisional of U.S. Patent Application No. 60/708,986, filed Aug. 17, 2005, which is incorporated herein by reference as if fully set forth.
| Number | Date | Country | |
|---|---|---|---|
| 60708986 | Aug 2005 | US |
