Method for manufacturing a camshaft for an internal combustion engine by expanding a tubular element with a high pressure fluid and simultaneously compressing the tubular element axially

In a method for manufacturing a camshaft for an internal combustion engine a metal tubular element is expanded within a mold with the aid of a fluid at high pressure fed into the tubular element and with a simultaneous axial compression of the tubular element. The cams of the camshaft are formed in subsequent steps, starting from intermediate cams and ending with end cams. In a first step of the method, the intermediate cams are formed in a first mold. In a subsequent step, the end cams are formed within auxiliary molds which surround, only throughout a predetermined length, end portions of the tubular element which project from the mold which surrounds the already formed intermediate cams. In this subsequent step, the tubular element is compressed axially by axially displacing two clamp members, which grip and surround completely, throughout a predetermined length, the end portions of the tubular element which project outwardly from the auxiliary molds.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application No. 14155616.7 filed on Feb. 18, 2014, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods for manufacturing camshafts for internal combustion engines, of the type in which a metal tubular element is expanded within a mould with the aid of a fluid at high pressure fed into the tubular element and by simultaneously compressing the tubular element axially.

In particular the invention relates to a method of the type in which the cams of the camshaft are formed in subsequent steps, starting from the intermediate cams to end with the cams at the ends of the camshaft.

A method of the above indicated type is disclosed for example in US 2003/0221514 A1. In the solution described in this document, the cams of the camshaft are formed by constantly feeding pressurized fluid into the tubular element and by simultaneously compressing the tubular element with the aid of punches axially pushed against the opposite ends of the tubular element. The cams are formed within corresponding cavities of the mould by heating locally and in sequence the different portions of the tubular element which must define the cams in the finished product. This solution does not ensure a precise and reliable control on the forming process of the various cams and is also relatively complicated and costly to be implemented.

OBJECT OF THE INVENTION

The object of the present invention is that of providing a method for manufacturing a camshaft for an internal combustion engine which is simpler and more reliable with respect to the known methods and through which in particular a camshaft which has the required dimensional and shape characteristics can be obtained with a good degree of precision and by simple and quick operations.

SUMMARY OF THE INVENTION

In view of achieving this object, the invention provides a method of the type indicated at the beginning of the present description, and further characterized in that:in a first step of the method, the intermediate cams of the camshaft are formed within a first mould which surrounds only the intermediate portion of the tubular element, said mould having a cavity with portions having a shape and dimensions corresponding to those of the intermediate cams to be obtained, the remaining part of said cavity having a cylindrical shape and a diameter corresponding to the outer diameter of said tubular element, said tubular element being arranged within said first mould, with its ends portions which project from said first mould,during said first step of the method, fluid at high pressure is fed into the tubular element and the tubular element is simultaneously compressed axially by moving two clamp members axially towards each other, which clamp members grip and completely surround, throughout a predetermined length, the end portions of the tubular element which project outwardly from said first mould,in a subsequent step of the method, the end cams of the camshaft are formed within auxiliary moulds which surround, throughout a predetermined length, the end portions of the tubular element which project outwardly from the mould which surrounds the already formed intermediate cams,said auxiliary moulds have cavities with portions having a shape and dimensions corresponding to those of the end cams to be obtained and the remaining part of the cavities having a cylindrical shape and a diameter corresponding to the outer diameter of said tubular element,said auxiliary moulds are initially arranged axially spaced apart from the opposite ends of the mould which surrounds the already formed intermediate cams, said tubular element having its end portions which project beyond said auxiliary moulds,during said subsequent step of the method, fluid at high pressure is fed into the tubular element, while the tubular element is simultaneously compressed axially by moving two clamp members axially towards each other, which clamp members grip and completely surround, throughout a predetermined length, the end portions of the tubular element which project outwardly from said auxiliary moulds,during said subsequent step of the method, said clamp members are pushed axially until they come in contact against said auxiliary moulds, and then they are kept to be pushed axially until they move said auxiliary moulds in contact against the mould which surrounds the already formed intermediate cams,so as to form the end cams of the camshafts, while the cavity portions which are for forming the end cams are brought to a final axial position, in which said cavity portions for forming the end cams are at a proper axial distance from the already formed intermediate cams.

Due to the above indicated features, the method according to the invention enables the camshaft to be obtained simply and quickly, through subsequent forming of the intermediate cams and then of the end cams, while ensuring a precise control on dimensions and shape of the finished product.

The forming operation with the aid of fluid at high pressure can be carried out with or without heating, by a liquid fluid (such as water or oil) or with the aid of a gas. For example, nitrogen at a pressure between 400 and 800 bars can be used, at a temperature between 800° C. and 900° C. Alternatively, the forming operation can be carried out with water or oil at a pressure of 5000-6000 bars, at ambient temperature or at a temperature greater than ambient temperature.

For example, the tubular element can be made of hardened steel, such as boron steel 22MnB5 or 27MnCrB5.

The invention is also directed to the device for carrying out the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIG. 1, reference number1generally designates a tubular element made for example of boron steel 22MnB5. In an actual embodiment, tubular element1had a length L=500 mm and inner and outer diameters d=27 mm and D=30 mm.

In the first step of the method shown inFIG. 1, the tubular element1is arranged within a mould2for forming the two intermediate cams of the camshaft, i.e. two cams C1, C2which are located at the intermediate shaft portion in the finished camshaft CS (FIG. 8).

As shown inFIG. 1, in the initial step of the method the tubular element1is positioned with its central portion located inside mould2and its end portions1a,1b, which project outwardly from the opposite ends2a,2bof mould2.

In the illustrated example, mould2is made of a central mould section3and two end mould sections4,5arranged at the two sides of the central mould section3. Mould sections3,4,5are each consisting of two half-moulds3a,3b;4a,4b;5a,5bwhich can be displaced between an opened condition (not shown) and a closed condition in which each pair of half-moulds clamps a corresponding portion of the tubular element1therebetween.

The present description and the annexed drawings do not include the details of construction of the press in which the above described moulds are positioned and the means for displacing each pair of half-moulds between their opened and closed conditions. These details of construction, taken alone, do not fall within the scope of the present invention and can be made in any known way. Moreover, the deletion of these details from the drawings renders the latter simpler and easier to understand.

Naturally, although the illustrated example has a mould2made of three mould sections3,4,5, theoretically a single pair of half-moulds could be provided, incorporating the three mould sections3,4,5.

In the closed condition of the half-moulds3a,3b,4a,4b,5a,5b, mould2defines a forming cavity with cavity portions c1, c2having a shape and dimensions corresponding to those of the intermediate cams C1, C2to be formed. For the remaining part, the forming cavity is a cylindrical cavity with a diameter corresponding to the outer diameter of the tubular element1. In the case of the illustrated example, the cavity portions c1, c2are defined by the half-moulds3a,3bof the central mould section3, whereas the half-mould of the end mould sections4,5define cylindrical cavities with a diameter corresponding to the outer diameter of the tubular element. Between the two cavity portions c1, c2, also the two half-moulds of the central mould section3define a cylindrical cavity with a diameter corresponding to the outer diameter of the tubular element1.

In the closed condition of half-moulds3a,3b,4a,4b,5a,5bwhich constitute mould2, these half-moulds surround completely and are clamped in contact with the intermediate portion of the tubular element1, except for the portions thereof located at the cavity portions c1, c2which are to form the intermediate cams C1, C2of the camshaft.

The half-moulds of mould2are clamped against the tubular element1with a force which may be for example of 500 tons, approximately.

During the forming step of the intermediate cams C1, C2shown inFIG. 1, pressurized fluid (such as water at 5000 bars) is fed into the tubular element1.

The details of construction of the means for feeding the pressurized fluid into the tubular element are not described nor shown herein, since they do not fall, taken alone, within the scope of the present invention and also because they can be made in any known way, the representation in the annexed drawings being evidently purely diagrammatic. It is believed that the deletion of these details from the drawings renders the latter quicker and easier to understand.

During said first step of the method according to the invention, the tubular element1is compressed axially while the pressurized fluid is simultaneously fed into the tubular element.

In the case of the invention, the axial compression of the tubular element1is obtained by providing two clamp members6,7which grip and surround completely, throughout a predetermined length, the end portions1a,1bof the tubular element1which project outwardly from mould2. Clamp members6,7are each consisting of two jaws6a,6b;7a,7bwhich define therebetween a cylindrical cavity having a diameter corresponding to the outer diameter of the tubular element1. The jaws of the clamp members6,7are clamped against the end portions1a,1bof the tubular element1by a force for example of 500 tons approximately. As shown inFIG. 1, in the initial step of the method, clamp members6,7are spaced from the opposite ends2a,2bof mould2. According to the invention, the clamp members6,7are displaced axially against each other (i.e. along the direction of the axis of tubular element1), until they come in contact with the opposite ends2a,2bof mould2, during the step for forming cams C1, C2, while pressurized water is fed into tubular element1.

Referring toFIG. 1, which is purely diagrammatic, pressurized water is fed (with the aid of means of any known type) from the right end of tubular element1, while the left end of tubular element1is closed, so that the pressurized water causes deformation of the wall of the tubular element1within portions c1, c2of the forming cavity, until the wall of the tubular element is pressed against the surface of said cavity portions c1, c2, thus forming two cams C1, C2. The displacement of material during this step is favoured by the axial compression of tubular element1which, as shown, takes place due to the action of clamp members6,7. These clamp members engage the end portions1a,1bof the tubular element1throughout a predetermined axial length and therefore they ensure that these end portions are kept at the initial dimension of the tubular element during this first step of the method. The same applies to the portions of the tubular element which are located within mould2but out of the two cavity portions c1, c2.

Due to the above described measures, the first step of the method according to the invention brings to forming a blank product having only the two intermediate cams C1, C2as shown inFIG. 5.

FIGS. 6, 7show the second step of the method according to the invention, which is required for obtaining the end cams C3, C4of the camshaft (seeFIG. 8).

In order to carry out the second step of the method, the two intermediate cams C1, C2which have been already obtained are kept within a mould2′ having a cavity copying the shape of these intermediate cams. In the case of the illustrated example, this mould2′ is made of the same central section3of mould2which has been used in the first step, completed with two end mould sections8,9which are arranged in replacement of the two end mould sections4,5ofFIGS. 1, 5. The central mould section3and the end mould sections8,9are each made of two half-moulds3a,3b;8a,8b;9a,9b. These half-moulds are pressed against the intermediate portion of tubular element1, during the second step of the method according to the invention, by a force for example of 500 tons approximately. The replacement of mould sections4,5with mould sections8,9is merely due to the need of adopting mould sections having a lower axial dimension. However, the solution shown herein constitutes only an exemplary embodiment of the invention, while it is clearly evident that, for example, in the case ofFIG. 6, in place of mould sections3,8,9a single mould section integrating the mould sections3,8,9could be used, which single mould section would be formed by two half-moulds clamped around the tubular element1.

In the second step of the method according to the invention, two auxiliary moulds10,11are further provided which surround, throughout a predetermined length, the end portions of the tubular element1which project outwardly from the mould defined by sections3,8,9. The auxiliary moulds10,11have forming cavities with portions c3, c4having dimensions and shape corresponding to those of the end cams C3, C4of the camshaft CS (seeFIG. 8). The remaining parts of the cavities of auxiliary moulds10,11(in the closed condition of these moulds) have a cylindrical shape and a diameter corresponding to the outer diameter of the tubular element1, so that in the closed condition in which the half-moulds10a,10b,11a,11bare pressed against each other, said auxiliary moulds10,11slidably engage the surface of the tubular element1and can be axially moved with respect thereto.

The auxiliary moulds10,11are initially arranged axially spaced apart from the opposite ends12,13of the mould which surrounds the already formed intermediate cams C1, C2(which mould is constituted by the mould sections3,8,9in the illustrated example). The tubular element1has its end portions1a,1bwhich project beyond the auxiliary moulds10,11.

During the subsequent step of the method, fluid at high pressure is fed into the tubular element1and the tubular element1is simultaneously compressed axially by displacing the two clamp members6,7axially towards each other, which clamp members are those which have been already described as being used in the initial step of the method. The two clamp members6,7, each consisting of the jaws6a,6band7a,7bas already indicated above, a grip and completely surround, through a predetermined length, the end portions1a,1bof the tubular element1which project outwardly from the auxiliary moulds10,11.

During this final step of the method, the clamp members6,7start from a position axially spaced apart with respect to the auxiliary moulds10,11. The clamp members6,7are pushed axially until they come in contact against the auxiliary moulds10,11and then are kept to be pushed axially towards each other, until they move the auxiliary moulds10,11against of the central mould which surrounds the intermediate cams C1, C2. In this step of the method, therefore the auxiliary moulds10,11are displaced by a length corresponding to the initial distance between the auxiliary moulds10,11and the opposite ends12,13of the central mould, whereas the clamp members6,7are displaced by an axial length corresponding to the sum of the two spacings shown inFIG. 6, that is the initial distance between the auxiliary moulds10,11and the opposite surfaces12,13of the central mould, and the axial distance between each clamp member6,7and the auxiliary mould10,11which is adjacent thereto.

Therefore, in this step of the method, the portions of the tubular element1which are to form the end cams C3, C4are expanded by the pressurized fluid fed into the tubular element, while the required flow of material is ensured by the axial compression of the tubular element1. The end cams C3, C4are thus formed while the forming cavities c3, c4are progressively brought to the final positions in which they are at the proper distance from the intermediate cams C1, C2which have been already formed. During this step, both the clamp members6,7and also the end mould sections8,9ensure that the portions of the camshaft adjacent to the cams (designated by1m,1n,1p,1qinFIG. 8) are kept to the proper dimension, corresponding to the outer diameter of the starting tubular element1.

Also with reference to the second step of the method which have been described above, the details of constructions are not given relating to the press for use of the moulds which have been shown herein only diagrammatically, since they do not fall, taken alone, within the scope of the present invention and also because they can be implemented in any known way. The same applies to the means which are used for pushing the clamp members6,7axially towards each other.

In the case of the embodiment shown herein, the cavity portions c1, c2, c3, c4for forming cams C1, C2, C3, C4are shaped so that each cam is formed with an axially intermediate portion whose surface has the required cam profile and two opposite end portions which are tapered progressively towards a confluence on the outer cylindrical surface of the shaft, from which the cams project. This shape is different with respect to that of conventional camshafts, in which each cam has two opposite end faces which are planar and orthogonal to the shaft axis. In this manner, proper operation of the camshaft is not jeopardized and at the same time an easier deformation of the wall of the tubular element1during the camshaft forming operation is possible.

Naturally, while the principle of the invention remains the same, the details of construction and the embodiments may widely vary with respect to what has been described and illustrated purely by way of example, without departing from the scope of the present invention.