Method for producing a compression connection

Abstract

A method for producing a compression connection for a driving part (1), in particular for an essentially ring-shaped driving part (1) on a shaft (3), in particular in the case of a built-up camshaft with which the driving part (1) has an opening that essentially corresponds to the outside diameter of the shaft (3), the driving part (1) sits on the shaft with coverage in the finished compression connection, an adhesive layer is applied between the circumferential surfaces of the driving part (1) and the shaft (3), is to be improved. To this end, such a method is characterized by the following features: the driving part (1) is heated until reaching the joining temperature and is thereby widened, the driving part (1) is pushed on to the shaft essentially without any forces.

Description

The present invention relates to a method for producing a compression connection for a driving part (e.g., cams, plugs, chain wheels, phase adjuster, bearings, . . . ), in particular for an essentially ring-shaped driving part on a shaft, in particular with a built-up camshaft according to the preamble of Claim 1.

For many years, casting was the dominant production technology for camshafts for passage vehicle engines. For many years, however, there have increasingly been camshafts of the built-up type of technology, whereby both technologies have their specific properties and advantages as well as preferred areas of use. For camshafts produced by the casting method, grey cast iron, for example, is considered as the starting material, but chilled cast iron is by far the most popular material for passenger vehicle engines. For the designs of built-up camshafts available on the market, there are various manufacturing technologies (MTZ volume 57, no. 5, May 1, 1996, pages 284-291). These built-up camshafts consist essentially of a pipe (solid or hollow rod) on which the driving parts are mounted by different methods. Among others, joining methods are described in which conversion layers are applied between the driving part and the shaft, and the joining can be performed by longitudinal or transverse compression connections, whereby the transverse compression connection is found to be a disadvantage with respect to the complexity of innovative equipment and the manufacturing tolerances that are difficult to maintain.

German Patent DE 197 03 260 describes a built-up crankshaft in which the cams and optionally also other add-on parts are connected to a shaft coated with a conversion layer via a longitudinal compression connection. This conversion layer may be designed as an adhesive layer. In this process, the cam is joined to a shaft cold and with a large coverage and thereby joined with high axial and radial forces. The disadvantage of this method is that due to the great coverage, great plastic deformations and stresses and therefore cracks are introduced into the system, which can no longer withstand the stresses in the valve drive. When the conversion layer is embodied as an adhesive layer, there is the additional disadvantage that the adhesive is displaced by the cam, which is joined with a great coverage and therefore the effect of the adhesive is lost entirely or at least has an extremely minor effect. Due to the minor adhesive effect to this extent, the high transferable torques required of future valve drives cannot be achieved adequately. Another disadvantage of this longitudinal compression method that should be mentioned here is that the shaft must be remachined at the bearing points in a complex operation after the joining process.

The present invention relates to the problem of providing an improved embodiment of a method for producing a compression connection for a driving part on a shaft, in particular in a built-up camshaft.

This problem is solved in a generic method according to this invention by the characterizing features of Claim 1.

This embodiment is characterized in that the driving part to be joined to the shaft by an addition of compression seating and adhesive seating is heated before being joined to the shaft and is therefore expanded and is thus characterized on the whole as a method involving no force, i.e., a joining method without coverage and thus avoiding plastic deformations and stresses and therefore cracks. Due to the joining method without force in which the driving part is pushed onto the shaft with practically no friction, the adhesive applied to the circumferential surfaces of the cam and/or the shaft is preserved without scraping any off, so that an optimal adhesive connection can be achieved. On the whole, this method yields an especially stable connection with which the cost and weight can be minimized while maintaining the same torques and therefore the energy expended at the required highest torques of a valve drive is lower on the whole, so this yields a connection that is especially secure under stress. Due to the application of adhesive, the hydrostatic pressure within the connection is increased on the one hand while on the other hand the connecting surface is increased due to the fact that the peaks in the surface roughness is filled out within the connection.

This yields on the whole an especially high strength of the connection, in particular a high shearing strength and therefore very high transferable torques. Measurements have shown that connections created by combining compression seating and adhesive seating can withstand a torque at least one-third higher.

Therefore, materials having low specifications, i.e., materials with a relatively low strength, can be used for the shaft while retaining the strength of the connection, or a low total use of material is possible with the same material; this has a positive effect on unit costs on the whole as well as the total weight of the shaft. Another great advantage in terms of unit costs is the fact that the energy required for the joining operation is kept low on the whole because small joining lengths and lower joining temperatures are possible, while at the same time achieving a connection having a high stability. In addition, this method does not require complex reworking of the shaft after the joining operation, so this also has a positive effect on unit costs and the total energy.

The driving agent is expediently heated by induction, hot air or radiation. Modern induction heating in particular can introduce energy into the driving part that is to be heated in a targeted manner, so that it can be heated to conform to demands. Induction heating generates an alternating magnetic field, which in turn induces an alternating current in the electrically conducting driving part. Because of the electric resistance of the driving part, this current induced in the driving part causes heating of same at the sites of where currents. With such induction heating, it is thus possible to introduce heat specifically at certain predefined locations through the shape of the inductor and/or by regulating the frequency used, so that heat is generated immediately and directly in the driving part itself, i.e., in its interior, and need not be conducted by thermal conduction, as is the case with a traditional oven which heats from the outside to the inside.

All the driving parts to be mounted on the shaft can be completely machined in advance so that no remachining of the driving parts and shaft is necessary after they are mounted on the shaft.

It is self-evident that the features mentioned above and those yet to be explained below may be used not only in the particular combination given but also in other combinations or alone without going beyond the scope of the present invention.

Preferred exemplary embodiments of the invention are shown in the drawings and explained in greater detail in the following description.

The figures show schematically:

FIG. 1 a schematic diagram of a driving part,

FIG. 2 multiple driving parts mounted on a shaft by the method according to the invention.

FIG. 1 shows a driving part 1, in particular a cam, having an essentially ring-shaped design equipped with a bulge 2. In addition, the driving part 1 has an opening 4 whose diameter corresponds essentially to the outside diameter of the shaft 3 shown in FIG. 2. To allow the driving part 1 to be arranged on the shaft 3 in a fixed manner, it is heated to create a compression connection by the inventive method until reaching a joining temperature, so that the diameter d of the opening 4 is increased. The widening of the diameter d of the opening 4 may be only large enough to allow the driving part 1 in the heated state to be pushed onto the shaft 3 directly without exerting any axial or radial forces and it solidifies on reaching a predetermined position and then is joined fixedly to the shaft 3. The application of the driving part 1 is thus limited according to this invention to the extent that the adhesive applied to the connection of the driving part 1 and/or the shaft 3 is not removed at all or not to any considerable extent in the joining operation.

Claims

1. A method for producing a compression connection for a driving part (1), in particular for an essentially ring-shaped driving part (1) on a shaft (3), in particular in the case of a built-on camshaft, wherein

the driving part (1) has an opening corresponding essentially to the outside diameter of the shaft (3),

the driving part (1) sits on the shaft with coverage in the finished compression connection,

an adhesive layer is provided between the circumferential surfaces of the driving part (1) and the shaft (3), wherein

the driving part (1) is heated until reaching the joining temperature and is thereby widened, and

the driving part (1) is pushed onto the shaft in an essentially force-free operation.

2. The method according to claim 1, wherein the shaft (3) is joined without after-working.