Method for manufacturing a camshaft

A camshaft has at least two completely machined individual cams fixedly mounted on a shaft in predetermined angular positions. The shaft includes an outside shaft and an inside shaft arranged concentrically in the former, and is to be manufactured in such a way that remachining of the joined camshaft is not necessary. This is by combining the individual cams even before they are mounted on a shaft and joining them to this shaft to form a machining module, such that the individual cams are combined in their mutual arrangement in relation to one another in which the cams are to be mounted on the finished camshaft. The final machining of the cams is performed within this machining nodule. When the cams are completely machined in this way, the cams are joined to the shaft of the camshaft within the machining module. This ensures that the desired mutual arrangement is maintained, i.e., that remachining is not necessary.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of German Application No. 10 2004 039 302.8 filed Aug. 13, 2004. Applicants also claim priority under 35 U.S.C. §365 of PCT/DE2005/001250 filed Jul. 15, 2005. The international application under PCT article 21(2) was not published in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a camshaft according to the preamble of patent Claim1.

2. The Prior Art

In the manufacture of camshafts in which the individual cams are not to be remachined after attaching and/or joining, one problem is how to join the individual cams accurately in the predetermined angular positions. Because of this difficulty, remachining is always necessary by grinding the cam contours after joining the individual cams or the tolerance limits of the cam positions must be determined by the joining process.

U.S. Pat. No. 5,664,463 A describes a method for manufacturing a camshaft, in which at least two individual completely machined cams are fixedly mounted on a shaft in predetermined angular positions, whereby the shaft may consist in particular of an outer shaft and an inner shaft arranged coaxially in the former.

European Patent 0 331 938 A describes how a subsequent machining of the contours of individual cams on a completely joined camshaft can be prevented if the cams are positioned accurately in assembly. The respective cams are each individual cams which are to be machined separately as individual cams.

U.S. Pat. No. 4,616,389 A describes a method for manufacturing a camshaft in which the cams are aligned on a mounting shaft in an arrangement corresponding to the final arrangement on the camshaft. After removing the mounting shaft, the aligned cams are chucked by another device for machining their boreholes. The completely machined cams are mounted on a respective shaft to form the camshaft being manufactured, namely by shrinking the cams onto the shaft.

According to U.S. Pat. No. 5,299,881A, the cams can be ground as a module. The ground cams are mounted individually on a shaft to produce a camshaft.

In a generic process for manufacturing camshafts, the present invention relates to the problem of eliminating remachining of the contours of the individual cams on the completely assembled camshaft.

In a generic manufacturing process, this problem is solved primarily through the process steps according to the characterizing features of patent Claim1.

Advantageous and expedient embodiments are the object of the subclaims.

The present invention is based on the general idea of combining the individual cams even before they are mounted on a shaft and joining them to this shaft to form a machining module, such that the individual cams are combined in their mutual arrangement in relation one another in which the cams are to be mounted on the finished camshaft. The final machining of the cams is performed within this machining module. When the cams are completely machined in this way, the cams are joined to the shaft of the camshaft within the machining module. This ensures that the desired mutual arrangement is maintained, i.e., that remachining is not necessary.

If only two cams are to be joined in a mutual fixedly predetermined arrangement on a shaft, then a corresponding machining module would consist only of these two cams and optionally axial spacers arranged between these cams.

SUMMARY OF THE INVENTION

Screws may be used as the means for joining the individual elements in a machining module for an axial bracing of the individual elements to one another, or after inserting dowel pins, screws may be used as tension means in machining and in joining. The screws may be in the form of countersunk screws. Instead of screws as tension means, any other tension means may be used when using dowel pins, such as the generally known tension means used in grinding and polishing.

With the inventive method, it is very advantageously possible to manufacture a camshaft having cams that are variably rotatable with respect to one another. In the case of one such camshaft known from European Patent 1 362 986 A1, for example, an inside shaft is mounted concentrically in an outside shaft, the two shafts being rotatable in relation to one another. First cams are fixedly connected to the outside shaft and second cams are fixedly connected to the inside shaft. These second cams are fixedly connected to the inside shaft, e.g., by connecting elements such as dowel pins that are secured in the inside shaft, penetrate through these cams radially and pass through the outside shaft through a recess provided there. Such second cams are rotatably mounted on the outside shaft. Subsequent machining of cams that have already been completely joined together—and are mutually adjustable to some extent—is difficult, so the inventive method has proven especially advantageous for this.

If a second cam, which must be provided with a radial borehole to receive a fastening element, e.g., a dowel pin, for an adjustable camshaft, is in a machining module to be thereby positioned within the finished camshaft and to be rotatable, then this borehole can be produced while the respective second cam is in the machining module. This ensures an accurate angular position of the respective second cam within the finished camshaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Two first cams1,2are joined together in one machining module, each first cam being situated on an outer end axially. Between these two first cams1,2there is a second cam4which is located at the center of the machining module and is spaced a distance axially away from the former via spacers3that are open at the circumference.

The total of three first and second cams1,2,4are linked together by two screws5that are approximately in opposition on the circumference. The two screws5are preferably designed as countersunk screws.

The cams1,2,4which are thus fixedly joined together in the machining module can be completely machined in this state, namely in particular with regard to their outside cam contours and their inside diameters.

The inside diameters of all the cams1,2,4are preferably selected to be the same in order to simplify machining.

The exemplary embodiment shown here concerns cams1,2,4for a camshaft having cams that are mutually variably adjustable with regard to their angular positions. The shaft belonging to cams1,2,4is made up of an inside shaft11and an outside shaft12, which surrounds the former concentrically (6). The two shafts11,12are rotatable in relation to one another. The relative rotation is usually accomplished by the fact that the inside shaft11is rotated inside the outside shaft12. The two first cams1,2which are situated on the outside axially in the machining module are intended for a tight seating on the outside shaft12. The second cam4, situated between these two cams1,2, is designed for a tight connection on the inside shaft11. In the case of the tight connection with the inside shaft, the second cam4is provided with an inside diameter which allows a rotatable play-free bearing of the second cam4on the outside shaft12(FIG. 6). The connection of the second cam4with the inside shaft11is accomplished by a fastening element which may be a dowel pin13. This dowel pin13is secured on one end in the fitting borehole7in the second cam4and on the other end in a borehole in the inside shaft11, also passing through a recess14in the form of an elongated hole in the outside shaft12. The fitting bore7of the second cam4is created while this second cam4is in the closed machining module.

The cams1,2,4have already been completely machined except for the machining operations performed while in the machining module.

After mounting the machining module on the outside shaft12of the camshaft, which is shown as an adjustable camshaft in the exemplary embodiment (FIG. 6), i.e., after the end of machining and when there is a connection, e.g., a shrink connection, between the first cams1,2and the outside shaft12, the machining module is opened and the screws5and the spacers3that are open on the circumference are removed. The boreholes10remaining in the cams1,2,4necessarily lead to the advantage of a weight reduction in cams having these boreholes10.

To accommodate the screws5, which are inserted as connecting means in a machining module, a thread8may advantageously be provided on the optional spacers3(FIGS. 3 through 5). In the case of such an embodiment, at least two screws5may be used in opposite directions axially with regard to their head position and thread position to ensure a play-free and detachable arrangement in relation to the cams1,2,4(FIGS. 3 through 5). Accordingly, the spacers3must have at least four boreholes, at least two of which are designed as through-bores and two of which are designed as a thread8. The advantage of this type of connection inside the machining module is first the possibility of reusing the spacers which are acted upon by the thread and are thus expensive and secondly the simpler machine-ability of all the cams1,2,4.

In order to be able to machine an adjustable second cam4in the machining module to an inside diameter that is the same as that of the other first cams1,2, the outside shaft12must have a recess9having a reduced diameter in the area in which the second cam4comes to lie (FIG. 6). The outside diameter of the outside shaft12is reduced to such an extent that the second cam4can be mounted on the outside shaft12rotatably and without any play in this area.

The radial circumferential surface of the cams1,2,4is understood to refer to their inside surfaces and the concentric outside surfaces and/or cam surfaces. The cam contours are especially important with respect to machining within the machining module.

With the finished adjustable camshaft illustrated inFIG. 6having an inside shaft11and an outside shaft12, the first cams1,2are tightly shrunk onto the outside shaft12. The rotatable second cam4, which is situated between these two first cams1,2and is rotatable with respect to them, is fixedly connected to the inside shaft11by a dowel pin13. To permit a relative rotation between the inside shaft11and the outside shaft12, the dowel pin13in the outside shaft fits through a recess14in the form of an elongated hole in the circumferential direction.

All the features described in the description and characterized in the following claims may be essential to the invention either individually or combined in any desired manner.