Method of producing a camshaft, as well as a camshaft made from a tube, and elements placed thereon

The present invention relates to a process for preparing an assembled camshaft from a shaft tube and pushed by elements a widening of the shaft tube in the region of the elements by axially limited hydraulic internal pressure is applied, wherein the material of an element associated Longitudinal section of the shaft tube in expanding total is subjected to a plastic deformation, during the Material of each element in the surface layer the accepting state a predominantly elastic deformation. In the mentioned deferred elements can around Cams, bearing rings and toothed or bevel gears act the rotation and angle exactly connected to the shaft tube must be.

There are known camshafts, finished where Cam and bearing rings by thermal methods be shrunk onto a shaft tube (DE-OS 33 01 749). Here, the choice of material of the elements is limited by that certain of the shrinking process specific the materials thermal expansion values ​​required are to produce the necessary fittings. Around a sufficient voltage between the shaft tube and elements ensure for a fixed connection, are certain also of the shaft material increased demands to provide strength and surface hardness. The Insert the shaft tube and the elements is due to the required temperature treatment lengthy and costly. The increase in temperature during joining is a hardness loss the elements inevitable.

Furthermore, there are camshafts are known in which individual Cam form-fitting pushed onto profiled rods and for example by shrinkage, freezing, soldering, welding or bonding are connected to these (DE-OS 23 36 241, DE-GM 79 20 957). Opposite conventional camshaft can hereby achieve any weight advantages, a conditionally change or adjust the angular position of the cam a complete transformation of the components.

In addition, it is known inside round cams and bearing seats define purely force fit on a shaft tube, by the shaft tube over its entire length by internal pressure is expanded, whereby to maintain the Press fit, in view of the thinly walled tube, the tube having must be filled a plastic compound (DE-PS 32 27 693). Without this additional measure, it is not yet possible been a safe torque-duty hard seat to create. The expansion over the entire length involves the risk of bulges in the areas between the cams, wherein at the end faces of the cams a notch effect can occur, the wave strength the decreases.

From FR-A-2351726 it is known to heat exchanger tubes through fully coated in sections hydraulic expansion set in holes in the tube sheet. The function of the Components and thus the component stress are very differently to judge. Evidence assessment of the deformation zone the heat exchanger tubes are not given.

The DE 34 09 541 A1 discloses a method for producing a hollow shaft with Kontruktionselementen as Gearwheels, cams or the like, in which the widened hollow shaft over its entire length and plastically is reshaped. The spaces between the elements In this case, over the diameter of holes in the elements also widened, thereby damaging shearing stresses may arise.

It is also known, a camshaft, comprising a hollow shaft and from provided with longitudinal or circumferential grooves To connect bearing seats and cams in that the shaft tube widened sections by means of internal pressure and is pressed into the grooves (DE-PS 25 46 802 and FR 2328108). Here are the cams uniform Wall thickness tubular configuration, so that a circumferential Fit on the shaft is impossible and thus the Strength of the cams does not appear as guarantees.

The present invention is based on the object of providing a A method of the kind mentioned for the preparation of a provide assembled camshaft, the easy and cheap is practicable and in which a shaft with high torque capacity for treating enlarged freedom in the selection of materials for the shaft tube and cam or is bearing seats possible.

The solution to this is a process which is is characterized in that the widening of the pipe in each case carried out on a longitudinal portion which on each side Length of the associated element by a supernatant from at least 50% and at most 150% of the wall thickness of the Tube exceeds, wherein the connection between the element and carried out the shaft tube in the motor circuit. I hereby ensures advantageously that complete and substantially same voltage clinging the pipe wall at the through hole of the element to the entire length takes place, whereby the risk of micro-slip reduced and the possibility of fretting corrosion is excluded. At the same time it is prevented that it to bulge the tube with notch effects on the may end faces of the elements. Special conditions result when several elements closely adjacent are, as in particular in so-called three- or Four-valve engines, ie or in an arrangement of three four valves per cylinder of the case. Here, the modify the effect process of the invention that the expansion of the shaft tube in a two or more Elements overlapping area is also completed. If so only up to a maximum free distance of the elements up to 40% of the wall thickness of the tube takes place, bulging of the tube is not to get and a uniform interference fit of the various elements ensured.

In this way, without thermal process steps Hard seats created that permit a torque transmission, up to 80% of the torsional strength of the shaft reached. As shaft material can thereby relatively low value Materials such as St 35 to St 52 used while great for the cams and bearing seats Materials can strength be used. impaired Joining the material values ​​not both materials. There establishing the call without external heat supply occurs and no heat treatment for annealing is required, neither shall a connection interfering material structural change nor a Loss of hardness on. The dimensional changes occurring during Expansion are - unlike in a heat treatment - calculable. The greater freedom of choice of material for the elements, improved matching of Cam material made of different strains will. There are here cams and bearing seats different materials can be used without the necessary torque transmission is at risk. Suitable Methods and devices for the hydraulic expansion individual longitudinal sections are easy and inexpensive represent. In a further advantageous manner remains by the novel process of the internal cross-section the shaft tube open to this way a shaft cooling to enable and internal lubrication of the bearing seats. The sheet produced by the present process Wave builds easily and, with appropriate consideration the joining operation without downstream grinding operations the cam or bearing seats are completed. The Representability smaller distances between the elements to be determined and the function adapted to the specific materials allow greater freedom in the corresponding Cylinder head design.

The inventive process is particularly illustrated perfectly when the difference U_min in between Shaft outside diameter d_a and element inside diameter D_i prior to expansion at least 0.9 times the external diameter, multiplied by the ratio of 0.2% - Yield strength R_p and Young's modulus E set becomes. In setting these values ​​will result in the desired resilient bias in the edge layer of Through opening of the force-fitting item specified.

After a favorable feature extends the plastic radial edge deformation in the through hole of the elements when using ductile material such as steel up to a material depth, about 10 to 15% of the least is radial wall thickness of the elements. This will achieves sufficient connection strength without the Strength of the elements is impaired. With hard Materials such as molding is a plastic deformation in the edge this magnitude is not possible nor necessary. In a further advantageous manner to occurring Elongation in the outer zone of the elements in the tangential Direction after the expansion of the order to 1% be adjusted to damage with additional loads excluded in use in the surface. Using ductile material such as steel is the preferred Range of values ​​for the elongation between 0.1 and 0.4%, while in case of brittle materials such as cast iron, the values ​​of elongation should be between 0.01 and 0.2%.

In conventional and effective manner that is inventive Process performed so that the expansion in the range hydraulic cams internal pressures 2000-3500 bar on the other hand, to widen the field of thin-walled shaft Bearing seats hydraulic internal pressures in the range of 1000 bar are applied to 2,500.

According to a preferred development is a material for the shaft tube having a lower by 25 to 35% of tensile strength selected relative to the material of the elements will. This favors the desired type of connection and allows the selection of relatively soft shaft materials for cost reasons.

As cam can favorably finished before joining Casting, steel or sintered elements are used, wherein materials of high hardness, the z. B. bearing steel to increase the lifetime of the finished camshaft can be selected without this strength the compound affected.

The above-described invention is in the application underlying idea on the onset of Hollow pin in holes, the joining of two pipes by means of a pipe sleeve or the joining of two of stacked shall apply mutatis mutandis pipe pieces. Some Details of the invention are appended by means of the Drawings illustrates.<dl tsize="8" compact="compact"><dt>Fig. 1A</dt><dd>shows a longitudinal section through a joint before joining cams and tube body</dd><dt>Fig. 1B</dt><dd>shows a splice according to Fig. 1a after put</dd><dt>Fig. 1C</dt><dd>shows a joint with two adjacent Elements after joining</dd></dl>

In the figures, each of the tube 1 and the mounted Element 2, in particular a cam 2a and a bearing bush with 2b designates. The in the claims and the description given lengths and Other sizes are available with the respective codes indicated.

In Fig. 1a is shown that the prior to the joining between Tube 1 and the cams 2, a circumferential gap 3 is present.

In Fig. 1b, the change in cross section of the tube is by joining recognizable, in particular the limited Length of the expanded tubular section 4 is clear.

In Fig. 1c is a flared pipe portion 4 is shown, the two adjacent deferred members 2a and 2b covers that have low free space 5 from each other have.