EP1107839B1 - Method for producing a camshaft and camshaft produced according to said method - Google Patents

Abstract

The aim of the invention is to produce cam shafts. To this end, the plasticising method known per se is combined with the internal high pressure deformation method in such a way that bearing elements, drive elements and control elements are produced at the ends by plasticising. Prefabricated supporting rings and chain wheels or gear wheels are mounted in a positive or non-positive fit by internal high pressure deformation. The inventive method can be mainly used for camshafts but also for producing shafts with cam plates etc.

Description

The invention relates to a method for producing camshafts and one according to camshaft manufactured using this method. It is preferably a Camshafts for engines for motor vehicles, but the method is also suitable for similar products, e.g. Cam discs arranged on a shaft manufacture. These are elements that have a rotational movement in a lifting movement implement by moving the lifting elements on rotating disks with different Run curvature and be moved against the direction of rotation.

Camshafts are known which are made in one piece, i.e. forged or are poured. The running surfaces of the cams, which are subject to wear, are after mechanical machining by laser beams, electron beams or TIG remelted or e.g. inductive or a thermal / chemical Process hardened. Then the further mechanical treatment takes place. e.g. the Grinding the bearings and cam shapes. These camshafts have the disadvantage that their weight and the mass to be moved are very high. The high mass of Camshaft adversely affects fuel consumption. Another disadvantage is the high mechanical effort involved in processing the blank.

It is also known to manufacture camshafts from individual parts. The single ones Cams are placed on the shaft, and preferably by welding connected, pressed or shrunk. Here is the lack of high Weight of the solid cam discs removed from one piece, because the shaft can be a hollow shaft, but the manufacturing effort is still very high.

In a further embodiment of the method it is also known the individual To attach cams on the hollow shaft by the hollow shaft after the Sliding on the cams is expanded by the application of pressure. As print media liquids are preferred. The pressure is applied using a piston or stamp generated (DE 34 09 541; 35 21 206; US 4 660 269; 5 259 268). However, this method has the disadvantage that the Production of the individual parts, in particular joining, is technologically complicated and restricts the inner contour of the cams.

It is also known to manufacture camshafts in such a way that an elongated one Hollow body, i.e. a hollow shaft by hydroforming - forming process (IHU process ) Forms acting as cams individually or one after the other or are generated simultaneously (DE-A-196 17 593).

Corresponding two-part or four-part tools ensure that Push the hollow shaft in the axial direction that defines the position of the cams arise and a one-piece molding takes place (WO 97/46341).

However, the camshaft manufactured by this method is deficient afflicted with the fact that the production costs compared to the forged or composite camshafts are lower, but the wear resistance of the Cam area is insufficient. It is not possible to use a material that Wear resistance ensures that the IHU process is practiced. Besides, it is not possible with a small distance between the cams on the shaft, as is usually the case with Automotive engines are required to produce a flat tread on the cams, because at the places of the highest degree of forming are inevitably weakened, which negatively affects the strength.

If a material is used for the hollow shaft, which reduces these defects contributes, this allows good deformation, but the hardness or Wear resistance cannot be achieved even by a subsequent hardening process. The hardness and wear resistance of the cams is a basic requirement for a long service life of the camshafts in the motor vehicle. It is also very difficult, though possible at all, in the entire area of the camshaft, i.e. the wave itself and especially the flanks and tips of the cam the necessary material thickness to reach.

It is also known that the tube sections forming the cam track with a produce eccentric profiling and this using a To strengthen the press fit network. The cam is manufactured by Explosive forming of a pipe. The individual cams are made accordingly attached to the camshaft offset to each other (DD 243 223). This currently Camshafts produced require a high manufacturing cost and have a high weight. The plastic forming process cannot be controlled depending on the time.

The invention has for its object a method for producing To create camshafts with which by using the known Internal high-pressure forming process can produce camshafts that are firm have low deflection, high torsional strength and high Have flexural rigidity in the load areas on the cam flank and tip. The manufacturing process should be simple. Applying an additional layer, i.e. Wear protection layer in a further process step should be omitted, as well elaborate mechanical rework. The use of materials should be low. The number the required items for the entire camshaft are said to be known Manufacturing processes for camshafts can be reduced.

According to the invention the object according to the features of claims 1 and 8 solved. Advantageous embodiments are in claims 2 to 7 and 9 to 17 described.

The essence of the invention is that in a separate process accordingly hard and wear-resistant support rings with a small wall thickness and final shape of the cam are produced by these support rings Internal high pressure forming (called IHU) placed in an IHU tool and through the IHU tool and axial forces introduced into the pipe in connection with over a pressure medium generates internal forces a one - or two - stage transformation of the Tube to the camshaft.

When the forming process is finished, the positive and positive connection takes place of the cam with the support ring. At the ends of the camshaft are in themselves known bearing elements arranged, which are attached in a conventional manner.

In a further advantageous embodiment of the method, in a Process stage, which precedes the aforementioned method, a tube from a Material that has the necessary properties for deformation and mechanical Requirements met by the known kneading, also called roller kneading, or that Upset, deformed in such a way that the pipe is wholly or partially or only the Camshaft ends plastically formed, e.g. ironed and / or thickened become. At the ends there are shaped elements for drive and control elements, e.g. the seat created for gears. In the following above Process stage is through the hydroforming process the pipe in the area in which the cams are arranged, expanded, with the support rings corresponding to the Positions of the cams are inserted.

In the case of cams that run very pointed, the support rings have the same wall thickness have the disadvantage that the tube is subject to a high degree of deformation and under A multi-stage forming process may be necessary. With that rise Manufacturing costs with falling productivity. Furthermore exist outside of Camshaft in the cylinder head Interfering contours between or next to the cam. Through it the available space is limited and the IHU process is made more difficult. This limitation is, if at all, only due to a complicated, multi-stage Eliminate IHU process. This in turn requires high manufacturing costs. Therefore there is an advantageous embodiment of the method, or of those produced thereafter Wave in that the support rings, which are manufactured in a separate process, correspond to the function-related contour on the outside and a slightly larger one on the inside Have diameter than the tube. The wall thickness of the support ring is not uniformly thick, but has a greater thickness in the area of the cam tip. This means that the support ring has a variable thickness as a cam and the inner contour is no circle.

The method according to the invention essentially consists of two or several well-known modern manufacturing processes can be combined.

It is advantageous to make at least one groove radially in the support ring in order to to prevent lateral displacement of the support ring by applying pressure fills this groove with material of the shaft.

Another advantageous embodiment of the method consists in that drive and / or control elements also attached to the shaft by the IHU method become. Storage areas can also be expanded by expanding the pipe through the IHU - Processes are generated. Especially those due to the plastic deformation process The resulting strain hardening of the pipe material is advantageous.

The camshaft produced by the method according to the invention is characterized by hollow cams and very thin-walled support rings in weight very light and owns high rigidity. There is the advantage that the support rings do not or only slightly mechanically reworked. Their hardness is according to the requirements already given what the usual subsequent hardening, e.g. induction hardening or remelt hardening in a vacuum process.

The further design of the method provides an additional advantage in that the round kneading or upsetting in connection with the IHU process in contrast to all known manufacturing processes a very low manufacturing cost and thus also requires low costs. Above all, these are reduced that the number of separate parts to be manufactured and then joined is very low. The manufacturing according to the invention eliminates sources of error that could occur due to the previous joining of end pieces. A major advantage The method also consists in the functional elements being kneaded can be produced in their geometry, dimensional accuracy and surface quality and a require very little mechanical rework. Often only one is required Grinding process for completion.

The camshaft produced by the method according to the invention consists of a small number of individual parts. With the end of the forming process, they are Cam rings non-positively and positively connected to the shaft.

It is also advantageous to insert the support ring on the side facing the tube bevelled on both sides. This also means that it moves sideways on the Prevents wave.

An advantageous embodiment of the support rings is that the support ring opposite the prior art consists of plastics or sintered materials. This Materials offer the advantage of simple manufacture at low manufacturing costs.

Ceramic materials can also be used. You have the advantage with the highest wear resistance and lowest weight, the lightest Manufacture camshaft.

Another advantageous embodiment of the camshaft is that the tube made of aluminum or titanium. This makes the camshaft very light.

Fig.1:

einen Längsschnitt durch eine fertige Nockenwelle,

Fig.2:

einen Querschnitt durch einen Nocken auf der Welle,

Fig.3:

einen Ausschnitt als Längsschnitt durch einen Nocken auf der Welle.

Fig.4:

eine Nockenwelle mit durch Rundkneten / Stauchen verformten Enden

Fig.5:

eine Nockenwelle mit Tragringen variabler Dicke im Schnitt

The invention is described using two exemplary embodiments. The associated drawings show in

Fig.1:

a longitudinal section through a finished camshaft,

Figure 2:

a cross section through a cam on the shaft,

Figure 3:

a section as a longitudinal section through a cam on the shaft.

Figure 4:

a camshaft with ends deformed by kneading / upsetting

Figure 5:

a camshaft with support rings of variable thickness on average

1 to 3 show the production of a camshaft by the IHU method.

On a thin-walled tube 1 made of a readily deformable material is by IHU deformation the camshaft is produced close to the contour in a press mold; i.e. the places where a cam 2 has its seat is according to the dimensions of the cam 2 and shaped their location. The shaft with its cam 2 is a single hollow body. In a known process independently support rings 3, as in Fig.2 and 3rd clearly manufactured. For example a tube made of wear-resistant material profiled that the final shape of the support ring 3 (cam) is given and hardened. The prefabricated tube 1 to be formed into the camshaft is formed by the Support rings 3 pushed and together with them in the open forming tool inserted. In this way, all individual parts are fixed in position. The forming tool is axially closed and radial the force application can be used for forming. The Force application begins with a defined axial force on the pipe 1 and / or Tool, supported by a defined internal pressure in the pipe 1. After the The tool is completely closed axially and radially using a pure IHU process the positive and non-positive connection of tube 1 and support ring 3. On the End of the tube 1 are bearing or drive elements 5 in a known manner applied. It is also possible to use the IHU process on tube 1 Fasten.

It is also possible to make a groove 4 radially in the interior of the support ring 3, whereby the hold on the cam 2 is improved by this groove 4 with the material the tube 1 fills. It is also possible to have the support ring 3 on the inside diameter Provide phases that fill with material in the final IHU process.

Another example is the manufacture of a camshaft by the IHU - Process described in combination with the kneading process according to FIG. 4.

The tube 1 made of a readily deformable material is deformed to thicken at its ends by kneading or upsetting. This reduces its inside diameter D _I on one side and produces its outside diameter D _A , so that a zone 6 reinforcing the camshaft is created. At the extreme end there is a functional element 7, the seat of which is brought to its final dimension by grinding. At the other end, the inner diameter D is likewise reduced by kneading or upsetting, at the same time as the kneading of the end already described, and a further functional element 7 (bearing seat, control cam, etc.) is created. In the following process section, the collar 8 is also upset, which is necessary for flanging on other units.
After the first process stage, the support rings 3, which are produced in a separate process and which correspond to the shape of the cams, and the sprocket (not marked) are attached in a force-fitting and positive manner by IHU processes.
For this purpose, the support rings 3 and the sprocket are placed in the hydroforming tool.

In Fig. 5 an embodiment of the camshaft is shown, in which the support ring 3 a has different thickness.

The tube 1 made of a readily deformable material has an outer diameter d _a . The support ring 3 made of sintered metal has the function-related shape on the outside and is not a circle on the inside. Its inner diameter D _i is slightly larger than the outer diameter d _{a of} the tube 1. The thickness of the support ring 3 is not constant. The height A, which would arise if one assumes a constant support ring thickness, is greater than the height A 'of the maximum deformation of the tube 1, and thus the radius R _i ' in the region of the deformation of the tube 1 is greater than R _i when assumed same thickness c of the support ring 3. In this area, the thickness c 'of the support ring 3 is greater and runs in the constant thickness c.

Although the support ring 3 in this form is slightly more expensive to produce, this means that the reduced costs for the hydroforming process, which will be possible in one step, outweigh.

Claims (17)

1. A method of manufacturing a camshaft from a tube (1), which is deformed by the action of axial forces and of a medium under high internal pressure, characterised in that bearing rings (3), which are produced in a separate process and correspond to the cam contour, the necessary hardness, strength and wear resistance, are inserted together with the tube (1) to be reshaped into an internal high pressure reshaping tool and that cams (2) are formed under the action of axial forces and of a medium under high internal pressure by expanding the tube (1) and the bearing rings (3) are connected to the cams (2) in a force- and form-locking manner.
2. A method as claimed in Claim 1, characterised in that, in a first method step before the internal high pressure reshaping, regions, preferably ends, of the tube (1), which are outside the region, in which the cams (2) have their seat, are squeezed and/or upset so that they are thickened and/or stretched and other functional elements are thus formed.
3. A method as claimed in Claim 1, characterised in that, in the first method step before the internal high pressure reshaping, between the ends of the camshaft, bearing surfaces and the subsequent regions, in which the cams (2) have their seat, are produced by round squeezing by reducing the diameter in this region to a desired value.
4. A method as claimed in Claim 1 or 2, characterised in that bearing surfaces are produced between cams (2) by internal high pressure reshaping by expanding the tube (1).
5. A method as claimed in at least one of Claims 1 to 4, characterised in that the bearing rings are hardened in a known manner before their insertion into the internal high pressure reshaping tool.
6. A method as claimed in at least one of Claims 1 to 5, characterised in that a toothed or chain wheel, produced in a separate process, is inserted into the internal high pressure reshaping tool and is connected in a force- and/or form-locking manner by the internal high pressure reshaping process.
7. A method as claimed in at least one of Claims 1 to 6, characterised in that after producing the thickened or narrowed ends of the camshaft by round squeezing, internal toothing and/or a screwthread is produced in an additional method step integrated with this method step.
8. A camshaft produced in accordance with Claim 1 which includes a tube (1) and functional elements, particularly cams (2), connected to the tube (1), characterised in that the cams (2) are formed close to shape by an internal high pressure reshaping method by deforming the tube (1) in shape and position, that a bearing ring (3) shaped in accordance with the cam contour comprising a hard, wear-resistant material is connected to the cam (2) in a force- and form-locking manner and that bearing and/or drive and/or control elements (5) are connected to the ends of the tube (1).
9. A camshaft as claimed in Claim 8, characterised in that the bearing rings (3) have the same wall thickness.
10. A camshaft as claimed in Claim 8, characterised in that the thickness of the bearing rings (3) is variable, whereby the thickness is greater in the region of the cam tips.
11. A camshaft as claimed in Claim 8, characterised in that the bearing ring (3) consists of sintered metal, plastic or ceramic material.
12. A camshaft as claimed in Claim 8, characterised in that the tube (1) consists of aluminium, magnesium or titanium or alloys thereof.
13. A camshaft as claimed in Claim 8, characterised in that the ends of the tube (1) are deformed by squeezing so that bearing surfaces, drive and/or control elements and internal and/or external screwthreads are produced by expanding or reducing the original diameter (D_i; d_a) of the tube (1).
14. A camshaft as claimed in Claim 8, characterised in that the drive and control elements, preferably chain or toothed wheels, are connected by an internal high pressure reshaping method.
15. A camshaft as claimed in Claim 14, characterised in that at least one radially extending groove (4) is made in the bearing ring (3) and drive and control elements.
16. A camshaft as claimed in Claim 14, characterised in that the side of the bearing ring (3) directed towards the tube (1) and the drive elements have bevels on one or both sides on the surface directed towards the tube (1).
17. A camshaft as claimed in Claim 8, characterised in that the bearing ring (3) is hardened before application to the shaped cam.

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