Valve drive for an internal combustion engine

The invention relates to a valve drive for an internal combustion engine. The drive has an elongated securing device or anti-rotation bridge which is referred to as a mounting aid. The device or bridge has receptacle spaces, arranged at intervals one behind the other, for valve tappets. A valve tappet, which is embodied as a roller tappet is arranged in each receptacle space and is secured with a tappet roller directed at a cam of a camshaft and in such a way that the valve tappet can be displaced longitudinally in the receptacle space at right angles to the longitudinal axis of the camshaft. The valve tappet is secured against rotation by two parallel planar key faces, which are formed on its outer surface and which bear against corresponding inner surfaces of the mounting aid.

In the United States, pushrod engines are still in widespread use as combustion engines. For any type of these engines there may be mounting aids for the roller tappets, embodied as either switchable tappets or as standard roller tappets. The respective roller tappets are pressed into a mounting aid and that aid is in turn mounted on the cylinder block. The present invention relates to a simple check as to whether the tappets are arranged in the correct position on the combustion engine.

In internal combustion engines it is known to use a plastic bridge to secure a roller tappet against rotation. The tappet is held in the plastic bridge by face-guiding means. Here, at least one planar face section is formed on the outer surface of the circular-cylindrical tappet, and it interacts with a corresponding planar surface section of a receptacle space of the mounting device. The mounting device may be a plastic part. In order to simplify transportation and mounting of the valve drive parts, the tappets are premounted on the mounting device with a pressure against the interfaces which are in mutual contact with one another.

A mounting device, in which the clamping of the tappets which is necessary for mounting is also effective during later operation of the engine when only the anti-rotation function is required, is disclosed in U.S. Pat. No. 5,088,455. That mounting aid or securing device is injection-molded from plastic with an appropriate glass-fiber reinforcement. However, the mounting aid or securing device is configured only for standard roller tappets, i.e. the positioning and the correct rotation of the tappets are of secondary importance.

As the fuel consumption and thus the emissions of pollutants of all engines also have to be reduced in the United States, future engines will be fitted with cylinder deactivation devices. Those respective cylinders which are to be deactivated are provided with switchable roller tappets which are different than normal tappets. In particular, in eight-cylinder engines, these switchable roller tappets are arranged irregularly with respect to the left-hand or right-hand banks of cylinders of a V8 engine in accordance with the ignition sequence.

Publication DE 197 12 610 A1 discloses a mounting device of an internal combustion engine of the type mentioned at the beginning and explains that combustion engines usually have roller valve tappets which engage with cam elevations of a camshaft. As the tappets cannot rotate about their longitudinal axis because the rollers have to remain on the tappets in the same plane as the cam elevations, the tappets are oriented in a suitable way in the cylinder block of the combustion engine with securing devices, and their rotation is prevented.

An object of the invention is to provide a securing device or mounting aid for the valve tappets of an internal combustion engine in which both standard roller tappets and switchable roller tappets can be mounted reliably at the correct points which are respectively assigned to them and the tappets having correct attitudes.

This object is achieved with the invention in that the mounting aid has both receptacle spaces with a first, e.g. relatively small, interval dimension of the two inner surfaces for bearing the keying faces of standard roller tappets and receptacle spaces with a second, e.g. relatively large, interval dimension of the two inner surfaces for bearing the keying faces of switchable roller tappets. The first and second dimensions may be reversed as to which is the larger, or other distinguishing profiling besides respective interval dimensioning may be selected.

A compression spring which surrounds the tappet and which is secured by means of a supporting plate and a Seeger ring may be arranged in the mounting aid in each receptacle space for a switchable roller tappet. The Seeger ring has a tongue which is integrally formed on its inner surface and which engages in a groove, corresponding in shape to the tongue, in the internal housing of the roller tappet.

Here, the Seeger ring may additionally have a tongue which is integrally formed on its outer surface and which engages in a cutout, corresponding to the shape of this tongue, in the mounting aid.

Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.

An exemplary embodiment of the invention is illustrated in the drawings and is described in more detail below.

FIG. 1 shows an end region of a mounting aid with an inserted switchable roller tappet in an end view;

FIG. 2 shows an end region of the mounting aid with an inserted standard roller tappet in an end view;

FIG. 3 shows a perspective view of the mounting aid;

FIG. 4 shows an end plan view of the mounting aid;

FIG. 5 shows a perspective view of a region of the mounting aid with an inserted switchable roller tappet;

FIG. 6 shows a longitudinal view of the switchable roller tappet inserted in the mounting aid; and

FIG. 7 shows a longitudinal section of the roller tappet which has been inserted in the mounting aid and rotated through 90° with respect to FIG. 6 .

A mounting aid 1 according to the invention which is illustrated in FIGS. 3 and 4 has along its length two receptacle spaces 2 for standard roller tappets 3 and two receptacle spaces 4 for switchable roller tappets 5 . As is apparent from FIGS. 1 and 2, planar inner surfaces 6 and 7 of the mounting aid 1 are formed for the securing positions of the roller tappets in the respective receptacle spaces 3 and 4 . The inner surfaces 6 interact in each case with keying faces 8 of the standard roller tappet 3 in a receptacle space 2 , with the standard roller tappet 3 being located in the receptacle space 2 . The inner surfaces 7 run in a receptacle space 4 , in each case parallel to keying faces 9 of the switchable roller tappet 5 which is arranged in the receptacle space 4 . The inner surfaces 6 and 7 therefore correspond to the respective keying faces 8 and 9 of the roller tappets 3 and 5 so that the mounting aid 1 can serve as an anti-rotation protection in the engine operating mode.

The keying faces 8 for the standard roller tappet 3 are on a smaller interval dimension than the keying faces 9 of the switchable roller tappet 5 . In the standard roller tappet 3 , a specific pressing dimension is ensured between the keying faces 8 and the inner surfaces 6 for mounting. As a result, the rollers of the roller tappet 3 continuously correspond to the cams provided for them on a camshaft.

With reference to FIGS. 1 and 2, if a standard roller tappet 3 is moved into the wrong position, i.e. into the receptacle space 4 , which is provided for a switchable roller tappet 5 , in the mounting aid 1 , the pressing dimension which is necessary to be able to mount the entire system composed of the tappet 3 and the mounting aid 1 is not provided. During the mounting process, the tappet 3 therefore drops out of the receptacle space 4 . It thus becomes clear that tappet 3 was in the wrong position. If the standard roller tappet 3 is in the correct position illustrated in FIG. 2, in which position the pressing dimension fits, the tappet 3 is held in its position so that the mounting aid 1 can then be screwed into the engine block.

Conversely, owing to the relatively small distance between the inner surfaces 6 of the receptacle space 2 , a switchable roller tappet 5 cannot be moved into the wrong position at all as there is too large an overlap between the key faces 9 with respect to the corresponding inner surfaces 6 as corresponding bearing faces in the mounting aid 1 . Therefore, the switchable roller tappet 5 cannot be pressed into the receptacle space 2 . The distance 10 between the inner surfaces 6 in the receptacle space 2 for standard roller tappets 3 is smaller than the distance 11 between the inner surfaces 7 in the receptacle space 4 for switchable roller tappets 5 .

Despite the fact that the installation length is the same, i.e. the pushrods of the valves are of the same length, the overall length of the switchable roller tappet 5 is greater than that of the standard roller tappet 3 . This makes it necessary, as shown in FIG. 3, to provide free spaces, i.e. the diameters of the drilled holes in the receptacle spaces 4 for the switchable roller tappets 5 must be expanded. They are larger than the diameters of the drilled holes in the receptacle spaces 2 for the standard roller tappets 3 .

FIG. 4 shows how a mounting aid 1 with mounted switchable roller tappets 5 and mounted standard roller tappets 3 may look in a view from above. It is necessary to ensure that each switchable roller tappet 5 is installed in the correct position, i.e. it is not turned in a mirror-inverted fashion under any circumstances, in order to ensure the corresponding supply of oil for the switching mechanism. For this purpose, a compression spring 12 (FIGS. 6 and 7) which is contained in the roller tappet and is what is referred to as a lost motion spring is secured by means of a supporting plate 13 and a Seeger ring 14 . Referring to FIG. 5, this Seeger ring then has two features which distinguish it from a standard Seeger ring.

The Seeger ring is positioned correctly with respect to the switchable roller tappet 5 as follows. An inner tongue 15 which is integrally formed on the inner surface of the Seeger ring 14 engages in a groove formed on the internal housing of the roller tappet 5 . As a result, the Seeger ring can only be mounted in the corresponding correct position. Otherwise, it cannot be moved into the groove provided for it. If the roller tappet 5 is mounted in the correct position, a further outer tongue 16 which is integrally formed on the outer surface of the Seeger ring 14 engages in a corresponding cutout in the mounting aid 1 in the position, and the roller tappet 5 can then be mounted with the correct attitude. If an attempt were to be made to install the roller tappet 5 in a position which is turned in a mirror-inverted fashion, that attempt would fail because the groove of the mounting aid 1 would then not be located in the region of the outer tongue 16 of the Seeger ring 14 .

As is apparent from FIGS. 6 and 7, it is necessary to prevent the tappet from being able to be rotated through 180° during the insertion of the roller tappet 5 in the mounting aid 1 . This can be avoided by suitably matching corresponding lengths, namely of the distance E of the Seeger ring 14 from the upper edge of the anti-rotation key faces 9 on the tappet 5 and the corresponding length of the corresponding bearing faces 7 in the mounting aid 1 . For this purpose, E must be smaller than F.

Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.