Shaft mechanism, in particular camshaft of automotive engines

A camshaft of an automotive engine includes two concentric contra-rotating shafts mounted one inside the other, namely an inside shaft and an outside shaft, at least one cam rotatably mounted on the outside shaft, fixedly connected to the inside shaft radially through the outside shaft via a fastening mechanism, a sleeve gripped by the fastening mechanism and inserted fixedly into aligned boreholes in the inside shaft and in the cam, a core that widens the material of the sleeve within its elasticity limits in the area of the inside shaft and is inserted into the sleeve after insertion of the sleeve into the shaft mechanism. To improve mountability, the core extends over the entire length of the sleeve and widens it beyond the area limited by the inside shaft without exceeding the upper limit of elasticity of the material of the sleeve in comparison with its uninstalled starting state.

This invention relates to a shaft mechanism, in particular a camshaft of automotive engines according to the preamble of Patent Claim1.

Such a shaft mechanism is known from European Patent EP 1 362 986 A1. The core, which causes widening of the mounting sleeve there, includes only the area of the mounting sleeve in which it is inside the area of the inside shaft. The end areas of the sleeve, which are situated inside the outside shaft and the cam connected to the inside shaft, are not included. The scope and purpose of the connecting device between the inside shaft and the cam, said connecting device consisting of a sleeve and a core inserted subsequently into this sleeve to widen it, are to have the option of mounting the connecting element in the inside shaft in such a way that no forces can be exerted on the inside shaft due to the mounting operation in such a way as to cause bending of the inside shaft. This is important in particular when the inside shaft is mounted inside the outside shaft in areas that are merely separated far apart axially and when there is a small radial play between the inside shaft and the outside shaft between these bearings and this radial play must not be lost due to bending of the inside shaft while the cam is fixedly connected to the inside shaft. In order for the inside shaft not to be bendable when the cam is connected to it, a sleeve from the fastening mechanism is inserted into a receiving borehole in the inside shaft, said receiving borehole having a diameter of such a size with respect to the outside diameter of the sleeve that the sleeve can be inserted into this borehole within the inside shaft without applying force. When the sleeve for fastening the cam is mounted, the core which widens this sleeve in the area of the inside shaft can be pressed in with axial support of the sleeve without thereby exerting axial forces on the inside shaft.

With the known shaft mechanism, the mounting sleeve is mounted via a fitting of the play in the inside shaft, so after they are assembled, there is already an overlap with respect to the cam material in the area of the cam, namely to such an extent that this already results in a finished, tight connection per se. Subsequent pressing on the core with the known mechanism serves only to widen the sleeve in the area of the inside shaft to achieve a tight seating of this inside shaft with respect to the sleeve, i.e., to achieve a condition without any play, e.g., a press fit with overlap in this area.

If multiple cams are to be connected to the inside shaft on a camshaft of a shaft mechanism distributed over the axial length thereof, then there may be a tolerance problem. This follows from the fact that in the case of a plurality of boreholes which must be aligned accurately with one another between the outside shaft and the inside shaft, this precision cannot always been maintained to the required extent. Due to deviations in dimensions with the mutually aligned boreholes of the inside shaft and cams, sticking may occur when the individual mounting sleeves are introduced inside the respective receiving borehole of the inside shaft, so that when the sleeves are inserted into the inside shaft, radial forces occur with respect to the inside shaft and can shift the latter out of its coaxial position inside the outside shaft. This can result in jamming between the inside shaft and the outside shaft. The present invention is related to eliminating these problems.

The problem on which the present invention is based is solved primarily by an embodiment of a generic shaft mechanism according to the characterizing feature of Patent claim1.

Advantageous and expedient embodiments are the object of the subclaims.

This invention is based on the following general idea.

The mounting device for connecting a cam to the inside shaft and the receiving bores in the cams and the inside shaft are coordinated with one another so that even if there is a minor misalignment between the boreholes of the cams on the one hand and the inside shaft on the other hand, unforced insertion of the mounting sleeve into the inside shaft can still be ensured with the greatest possible reliability and without applying force even in the case of a relatively long camshaft with multiple cams to be mounted over the length of the shaft.

Due to the measure according to Patent claim1, the desired security after a force-free introduction of the mounting sleeve into the inside shaft is achieved already due to the fact that the sleeve in the cams has a tight seating that is not yet ready for operation already at the point of introduction into the cam. This already greatly reduces the risk of jamming of the mounting sleeve on introduction into the inside shaft. The tight seating which is not yet adequately achieved in a manner that is reliable in operation at the time of introduction of the mounting sleeve into the cam is achieved according to the present invention through the subsequently inserted core, which extends over the entire length of the mounting sleeve.

Due to the fact that the core extends over the total length of the sleeve, it is extremely easy to secure its position inside the sleeve in the manufacturing process. When the core is flush with the sleeve with respect to its length, it can easily be pressed into the position in which it is aligned with the sleeve.

The sleeve and the receiving bores in the inside shaft and the outside shaft are advantageously coordinated so that there is a greater widening of the sleeve on the finished shaft mechanism in the area of the inside shaft than in the areas radially outside the inside shaft. The differences in the sleeve widening over the length of the sleeve can be supported by the shape of the core by the fact that it has, e.g., conically tapering end areas within the cam to be secured.

An especially advantageous embodiment of the present invention consists of the fact that the sleeve has wall perforations especially in the area in which it forms a press fit inside the inside shaft, so the elasticity of the sleeve can be relatively high in this area if no core has yet been inserted there. The advantage of such an elasticity is that even when there is a minor misalignment of the boreholes in the cam and the inside shaft, high clamping forces which could cause bending of the shaft cannot occur on insertion of the sleeve into the inside shaft. The respective wall passages are designed in particular as slots running so they are axially parallel to the sleeve.

A special form with respect to the inventive wall passages in the sleeve is a sleeve having longitudinal slots over its entire length. Such a sleeve having longitudinal slots has an especially great elasticity in installation and therefore can be installed with practically no application of force, in particular even when there is a minor misalignment of the boreholes involved in the connection.

In the case of a camshaft as the shaft mechanism consisting of two concentric shafts one inside the other, namely an inside shaft1and an outside shaft2, a cam3is rotatably mounted on the outside shaft2. The cam3shown here is the axial ring-shaped connecting area of a double cam (not depicted in the figure to this extent). The cam3is connected to the inside shaft1via a mounting mechanism5by means of a radial recess4in the outside shaft2.

The mounting mechanism5consists of a sleeve6having longitudinal slots, i.e., a sleeve6having a continuous longitudinal slot8and a core7pressed into the sleeve6. The core7is practically a cylindrical pin. The ends of the core7each taper in a slightly conical shape. The conical taper is so minor that it cannot be seen in the drawing. The length of the core7is designed so that it extends over the entire length of the sleeve6.

A uniform elastic deformation of the sleeve material can be achieved over the entire length of the sleeve6due to the areas of the core7tapering conically at the ends when using a sleeve6having a constant inside and outside diameter with different fits with regard to the diameter in the receiving boreholes of the inside shaft1on the one hand and the cams3on the other hand. The assembly of camshaft with a cam3mounted to rotate on the outside shaft2is performed as follows:

In a first assembly step, the inside shaft1is pushed into the outside shaft2. Then the mounting sleeve6is inserted through the borehole of a cam3pushed onto the outside shaft2and passed through the inside shaft1. The sleeve6is a cylindrical tube having a uniform inside diameter and outside diameter over the total length. The boreholes in the inside shaft1on the one hand and a cam3on the other hand into which the mounting sleeve6is inserted are coordinated in terms of diameter with the outside diameter of the mounting sleeve6so that the sleeve can be inserted while applying the least possible force. Different fits in the area of the inside shaft1and the cam3are then preferably achieved, with a tighter fit being selected in the area of the cam3than in the area of the inside shaft1. The ends of the pin-shaped core7taper conically so that despite the different fits in the area of the inside shaft1and/or the cam3as described above, a uniform elastic deformation of the sleeve6is achieved due to a core7, which is beneath the overlap in the sleeve6.

The tight seating between the sleeve6and the inside shaft1on the one hand and the cam3on the other hand is achieved due to an elastic widening of the sleeve material6by the core7which is situated in this sleeve in the overlap. The core7is pressed into the sleeve6in such a way that the radial forces occurring there are absorbed directly by the sleeve6, so that in particular no radial forces can act on the inside shaft1with the introduction and activation of the holding properties of this device on the inside shaft1.

All features described in the description and characterized in the following claims may be essential to the present invention either individually or combined in any form together.