The invention relates to a shaft-hub connection, in particular of assembled camshafts (10) for combustion engines, at which at least two functional parts (14, 16, 18) are shrunk or pressed onto corresponding rotationally symmetric shaft sections (24, 26, 28) with the hub thereof, wherein in an assembly direction (30) of the functional parts (14, 16, 18), the first section (24) is designed with a larger exterior circumference than the second section (26). According to the invention, the exterior circumference of the first shaft section (24) has a configuration, which varies between two base circles (dImin) and (dIf), over which first shaft section (24) the second functional part (16) with a corresponding interior circumference can be slid, which varies between two base circles (DIIf) and (DIImax), wherein in the assembly state the smaller base circle (DIIf) and the larger base circle (DIImax) of the second functional part (16) have a larger dimension than the corresponding base circles (dIf) and (dImin) of the first shaft section (24).

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is the U.S. National Stage of International Application No. PCT/EP2010/001761, filed Mar. 20, 2010, which designated the United States and has been published as International Publication No. WO 2010/108636 A1 and which claims the priority of German Patent Application, Serial No. 10 2009 014 895.7, filed Mar. 25, 2009, pursuant to 35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

The invention relates to a shaft-hub connection, in particular for assembled camshafts for internal combustion engines.

Shaft-hub connections wherein the respective functional part is affixed on the shaft with a press fit or a shrink fit are known from several technical applications. For example, it is known to affix the individual cams of assembled camshafts for internal combustion engines on the shaft with a press fit or a shrink fit. However, this requires that the respective sections of the shaft for the cams have a stepped or at least identical exterior diameter when viewed in the assembly direction. If structural considerations require a configuration where a section of the shaft has a smaller diameter in the assembly direction than the previous section, then the corresponding functional part can no longer be pressed on or shrunk on, because the functional part cannot be pushed across the section with the larger diameter.

It is therefore an object of the invention to propose a shaft-hub connection of the generic type, wherein a functional part of a section of the shaft having a smaller diameter can nevertheless be connected by a press fit or a shrink fit with only slightly increased complexity.

SUMMARY OF THE INVENTION

This object is attained according to the invention by a shaft-hub connection, comprising: a shaft comprising a plurality of rotationally-symmetric shaft sections; and at least two functional parts having associated hubs, wherein the at least two functional parts are connected to corresponding shaft sections by a shrink fit or a press fit, and wherein a first shaft section is formed with a greater exterior diameter than a second section in an assembly direction of the at least two functional parts, wherein an exterior circumference of the first shaft section has a configuration which varies between a first and a second base circle, wherein a second of the at least two functional parts is slid onto the first shaft section with a corresponding interior circumference that varies between a smaller base circle and a larger base circle, and

wherein when the at least two functional parts are connected to corresponding shaft sections, the smaller base circle and the larger base circle of the second functional part are sized to be greater than the corresponding second and first base circles of the first shaft section.

It is therefore proposed that the exterior circumference of the first section of the shaft has a configuration with two base circles dIminand dIf, over which the second functional part with a corresponding interior circumference with two base circles DIIfand DIImaxcan be slid. In the connected state, the smaller base circle DIIfof the second functional part corresponds to the exterior diameter dIIfof the second section of the shaft, whereas the larger base circle dIfof the first section of the shaft corresponds to the interior diameter DIfof the first functional part. The second functional part located in the assembly direction therebehind can then be slid over the first section of the shaft during assembly and subsequently affixed on the second section of the shaft by a press fit or a shrink fit.

In a preferred embodiment of the invention, the exterior circumference of the first section of the shaft and the interior circumference of the second functional part can be constructed with axis-parallel grooves and ribs. The second functional part can then be slid over the first section of the shaft, wherein the ribs of the second functional part engage in the grooves of the section of the shaft, or vice versa.

In an alternative embodiment, the exterior circumference of the first section of the shaft and the interior circumference of the second functional part can be provided with a spline, wherein the number of teeth, the shape of the teeth, etc., may be suitably adapted to the specific requirements of the connection.

To ensure an uncomplicated assembly of the functional part, it is proposed to construct the greater base circle DIImaxof the second functional part and its smaller base circle DIIfwith play relative to the corresponding base circles of the first shaft section. In this way, the second functional part can be slid over the first shaft section without applying a force.

In addition, for easy and cost-effective assembly, the exterior circumference of the second section of the shaft and the interior circumference of the first functional part can be constructed as smooth cylinders.

The carrying portion (in percent) between the respective partners of the connection section of the shaft: functional part is in a range from 80:20 to 20:80, in particular at 50:50.

Lastly, in an assembled camshaft for internal combustion engines, at least one functional part may be a cam which is shrunk or pressed onto the shaft in the assembly direction subsequent to another cam or another functional part.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 4show partially a camshaft10for internal combustion engines, with a shaft12on which several cams14,16,18(indicated inFIG. 1by a dashed line) are arranged.

The shaft12has sections20,22which form connecting sections or rotationally-symmetric bearing sections. Rotationally symmetric sections24,26,28of the shaft12which carry the aforementioned cams14,16,18are directly adjacent to the sections20,22. InFIG. 1, the cam14is seated in a first connection I on the shaft section24with an interference press fit. Likewise, the cams16,18are seated on associated shaft sections26,28in a second and third connection II, III.

Due to the structure of the shaft12, the bearing section20has the greatest exterior diameter, so that the cams14,16,18cannot be slid onto the shaft12from this side.

Moreover, the exterior diameters of the sections24,26carrying the cams14,16are constructed such that the exterior diameter dIIfof the center shaft section26is smaller than the exterior diameter dIfof the first shaft section24.

The cams14,16,18are connected to the shaft12and its supporting sections24,26,28from the side of the shaft12facing away from the bearing section20. This is performed with a press fit or a shrink fit, wherein the exterior diameters dIfand dIIfof the sections24,26,28are manufactured in a conventional manner with an oversize relative to the bores of the hubs of the cams14,16,18and are either pressed on or heat-shrunk.

For installing the cams16of the center section26with the aforementioned connection, the first section24of the shaft12is in the assembly direction (arrow30) constructed with an exterior circumference that has a smaller base circle dImin(seeFIG. 2) and a greater base circle dIf.

The shaft section24is hereby provided with a spline32, wherein the tip diameter forms the larger base circle dIfand the root diameter forms the smaller base circle dImin. The base circle dIminis hereby slightly smaller by a measure b than the exterior diameter dIIfof the section26of the shaft12.

Moreover, the hub of the second cam16, as viewed in the assembly direction30, is constructed with a corresponding spline34(seeFIG. 3), with the smaller base circle DIIfof the spline34being formed by the tip diameter and the larger base circle DIImaxof the spline34being formed by the root diameter. The diameter of the larger base circle DIImaxagain slightly larger by a measure a than the exterior diameter dIfof the section24of the shaft12.

The exterior diameter dIfof the first shaft section24and dIIfof the center shaft section26are also referred to as functional diameters, onto which the cams14,16with their corresponding functional diameters DIfand DIIfare slid. For sake of clarity of the Figures, the base circles of the cams16and of the first shaft section24are not drawn to scale.

The spline32,34is constructed with rounded tip regions and feet root regions of the teeth. The spline is also manufactured symmetrically such that the carrying portion (in percent) between the hub of the cams18,16on the sections28,26is 50:50.

Instead of the spline, the section28may also have an exterior circumference formed of ribs and grooves, whereas the hub of the cam16has a mating interior circumference. However, other, for example undulated configurations of the circumference forming two base circles dIfand dIminand DIImaxand DImaxmay be employed.

The connecting partners of the first section24of the shaft12and of the second cam16are constructed as simple smooth cylinders. For example, the first section26is machined to size by turning or grinding, whereas the hub of the cam28is precision drilled or honed.

The exterior circumference of the first shaft section24produced with two base circles dIf, dIminis formed, for example, by a rolling tool, and the exterior diameter dIfis subsequently ground to size; the interior diameter DIIfof the hub of the cam16is precision drilled and subsequently expanded by clearing to DIImaxor slightly larger.

To connect the two cams14,16on the sections24,26, the exterior diameter dIfof the section26is produced with the size of the interior diameter DIIfof the cam16and the exterior diameter dIfis produced with the interior diameter DIfof the cam14with a slight dimensional overlap.

Conversely, the smaller base circle dIminof the section24is slightly smaller by the measure b than the interior diameter DIIfof the cam16. Moreover, the larger base circle DIImaxof the cam16is slightly greater by the measure a than the exterior diameter dIfof the section24.

As a result, the second (center) cam16can be slid over the section24during assembly without applying a force, with the spline32,34engaging accordingly.

The cam16can then be shrunk the section26of the shaft12. The firm seat is attained by the dimensional overlap between dIIfand DIIf.

The cam16is subsequently shrunk on or pressed on to the section24, wherein the firm seat is attained by the dimensional overlap between dIfand dIf.

The invention is not limited to the illustrated exemplary embodiment. Other assembled shaft-hub connections aside from a camshaft may be constructed in a similar fashion. The cams16and/or the cams18can also be formed by another functional part, for example an eccentric part, a worm wheel, etc.