Method for manufacturing an assembled camshaft

Abstract

A method for manufacturing an assembled camshaft for valve-controlled internal combustion engines, in which at least one cam disc with a base circle region and cam region is machined on the running surface and has a cam-disc recess, includes shrinking the cam disc onto a corresponding shaft designed with a defined dimensional overlap by cooling the shaft and heating the cam disc. Temporally before being shrunk onto the shaft, the at least one cam disc is clamped by a clamping device such that a tension force acts on the recess wall region, which defines the cam-disc recess, the tension force corresponding to a predetermined extent to the state of stresses and/or deformation state of the recess wall region after the operation of shrinking the cam disc onto the corresponding shaft. The running-surface machining of the at least one cam disc takes place when the cam disc is clamped by the clamping device.

Claims

1. A method for manufacturing an assembled camshaft for valve-controlled internal combustion engines, the assembled camshaft including a shaft and at least one cam disc with a base circle region and a cam region, the method comprising: shrinking the at least one cam disc onto the shaft by a cam-disc recess designed with a defined dimensional overlap with the shaft; temporally before said step of shrinking, clamping the at least one cam disc by a clamping device so that a tension force acts on a recess wall region of the cam disc recess, the tension force corresponding to one of a state of stresses and a deformation state of the recess wall region after the at least one cam disc is shrunk onto the shaft; and machining the at least one cam disc by a running-surface-machining device when the at least one cam disc is clamped by the clamping device, wherein the step of clamping includes pushing the at least one cam disc by the cam-disc recess onto a tension tube region of a tension tube of the clamping device, and expanding the tension tube at least in the tension tube region with the cam-disc recess by a corresponding application of force such that the tension tube region is directed outward in the direction of the cam disc and the tension force is exerted on the recess wall region of the cam disc, and the step of expanding comprising acting, by a pressure medium source, on the tension tube by a pressure of a defined magnitude with a pressure medium to expand the tension tube in an elastic deformation range of the tension tube; and providing the tension tube of the clamping device with a varying wall thickness in at least one of an axial direction and a circumferential direction of the tension tube so that different tension forces distributed over a circumference of the recess wall region are generated during the step of expanding.

2. The method according to claim 1, wherein the step of shrinking includes cooling the shaft and heating the cam disc.

3. The method according to claim 1, wherein the step of clamping further comprises heating the clamping device.

4. The method according to claim 1, wherein the at least one cam disc is held in a position by aids temporarily applied to the clamping device temporally before the at least one cam disc is clamped.

5. The method according to claim 1, wherein, during the steps of clamping and machining, the at least one cam disc with the cam-disc recess is clampable on the clamping device so that a tension force acts on the recess wall region of the cam disc recess, the tension force acting on the recess wall region corresponding to a predetermined extent to at least one of a state of stresses and a deformation state of the recess wall region when the at least one cam disc is shrunk onto the corresponding shaft.

6. The method according to claim 1, wherein the step of providing includes providing the tension tube of the clamping device with a varying wall thickness in the circumferential direction of the tension tube.

7. The method according to claim 1, wherein the step of providing includes providing the tension tube of the clamping device with a varying wall thickness in the axial direction of the tension tube.

8. The method according to claim 1, wherein the tension tube has a first closed end and a second end connected to the pressure medium source.

9. The method according to claim 8, wherein the pressure medium is a hydraulic pressure medium.

10. The method according to claim 1, wherein said step of clamping comprises clamping a plurality of cam discs on the clamping device and the step of machining comprises machining the plurality of cam discs simultaneously on the clamping device.

11. The method according to claim 10, wherein the plurality of cam discs are cam discs that are to be shrunk onto a common shaft to produce the assembled camshaft.

12. A method for manufacturing an assembled camshaft for valve-controlled internal combustion engines, the assembled camshaft including a shaft and at least one cam disc with a base circle region and a cam region, the method comprising: shrinking the at least one cam disc onto the shaft by a cam-disc recess designed with a defined dimensional overlap with the shaft; temporally before said step of shrinking, clamping the at least one cam disc by a clamping device so that a tension force acts on a recess wall region of the cam disc recess, the tension force corresponding to one of a state of stresses and a deformation state of the recess wall region after the at least one cam disc is shrunk onto the shaft; and machining the at least one cam disc by a running-surface-machining device when the at least one cam disc is clamped by the clamping device, wherein the step of clamping includes pushing the at least one cam disc by the cam-disc recess onto a tension tube region of a tension tube of the clamping device, and expanding the tension tube at least in the tension tube region with the cam-disc recess by a corresponding application of force such that the tension tube region is directed outward in the direction of the cam disc and the tension force is exerted on the recess wall region of the cam disc, and the step of expanding comprising acting on two male cones in opposite directions by a pull rod and a push rod to interact, respectively, with female cones of the tension tube, said step of expanding comprises oppositely directed actuation of the pull rod and the push rod so that the tension tube is expanded with the tension force.

13. The method according to claim 12, wherein the step of shrinking includes cooling the shaft and heating the cam disc.

14. The method according to claim 12, wherein the step of clamping further comprises heating the clamping device.

15. The method according to claim 12, wherein the at least one cam disc is held in a position by aids temporarily applied to the clamping device temporally before the at least one cam disc is clamped.

16. The method according to claim 12, wherein, during the steps of clamping and machining, the at least one cam disc with the cam-disc recess is clampable on the clamping device so that a tension force acts on the recess wall region of the cam disc recess, the tension force acting on the recess wall region corresponding to a predetermined extent to at least one of a state of stresses and a deformation state of the recess wall region when the at least one cam disc is shrunk onto the corresponding shaft.

17. The method according to claim 12, further comprising the step of providing the tension tube of the clamping device with a different wall thickness in at least one of an axial direction and a circumferential direction of the tension tube so that different tension forces distributed over a circumference of the recess wall region are generated during the step of expanding.

18. The method according to claim 12, wherein said step of clamping comprises clamping a plurality of cam discs on the clamping device and the step of machining comprises machining the plurality of cam discs simultaneously on the clamping device.

19. The method according to claim 18, wherein the plurality of cam discs are cam discs that are to be shrunk onto a common shaft to produce the assembled camshaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Two exemplary embodiments of the invention are explained in more detail by way of example with reference to the attached, schematic drawing, in which:

(2) FIG. 1 is a cross-section diagram showing the individual parts of an assembled camshaft with a tubular shaft and a cam disc;

(3) FIG. 2 shows the assembled camshaft with the cam disc, which is shrunk onto the shaft, in a cross section according to line II-II from FIG. 3;

(4) FIG. 3 shows the assembled camshaft in a longitudinal section along the line III-III from FIG. 2;

(5) FIG. 4 is a cross-section of a clamping device with a hydraulically expandable tension tube for machining the running surface of the cam disc of the assembled camshaft; and

(6) FIG. 5 is a cross-section of a further clamping device with a tension tube which is expandable mechanically via cones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) A shaft 2 and an individual cam disc 3 of an assembled camshaft 1 for internal combustion engines, in particular for motor vehicles or commercial vehicles, are illustrated in a roughly schematic manner and only in part in FIG. 1, wherein the cam disc 3, as is apparent in FIGS. 2 and 3, is shrunk onto the shaft 2.

(8) For this purpose, the shaft 2, which is of tubular design here by way of example and is manufactured, for example, from steel or light metal, and with the outside diameter D thereof in a dimensional overlap with the inside diameter d of the cam disc 3 which, for example, is of the same material. The cam disc 3 has a cam-disc recess 3a which is bounded by a recess wall region 3b and is preferably formed by a bore. The shrinking-on operation takes place by appropriate temperature control of the cam disc 3 and shaft 2, for example by cooling the shaft 2 and simultaneously heating the cam disc 3, and by subsequently threading the cam disc 3 or a plurality of cam discs 3 onto the shaft. After the temperature of shaft 2 and cam disc 3 is equalized, a ready assembled camshaft 1 with a defined cam-running-surface geometry is present.

(9) FIGS. 2 and 3 show in greatly exaggerated form the deformations which are possible during the shrinking-on operation by the material stresses which occur when the temperature of the components 2, 3 is equalized and which can occur in particular in the cam-base-circle region of the cam disc 3 (low wall thickness) and can lead, for example, to a lifting curve error a (FIG. 2, indicated by dashed lines) or to a concave running surface b, as viewed in cross section (FIG. 3), with the risk of edge loads.

(10) This would result in the running surface of the cam disc 3, on which a valve-actuating element, such as a tilting lever, a tilting lever roller, a bucket tappet, etc., runs during the operation of the internal combustion engine, having to be remachined, in particular reground, in order preferably to ensure a slightly convex running surface and a precisely defined cam geometry.

(11) In order to avoid the deformations, which are illustrated in exaggerated form in FIGS. 2 and 3, of the cam disc 3 or of the running surface thereof, during the manufacturing of the cam disc 3 use is made of a clamping device 4 which is illustrated by way of example in FIG. 4 and, for example, forms part or a functional part of a running-surface-machining device or station (not illustrated) in which the running surface of the cam disc 3 is finished, in particular ground. For example, the running-surface-machining device can preferably be formed by a grinding machine, in particular by a contour grinding machine.

(12) The clamping device 4 has a tension tube 5 which is preferably of thin-walled and/or metallic design and has an integrally formed fastening flange 6 via which said tension tube can be connected to the running-surface-machining device.

(13) The tension tube 5 is designed to be closed on one end side 5a thereof and to be open towards the fastening flange 6 and can be acted upon with hydraulic medium of high isostatic pressure (arrows P) through the fastening flange 6 via a pressure connection 7.

(14) As shown in the exemplary embodiment, the tension tube 5 can have a different wall thickness and optionally can also be designed with a wall thickness which is different (noncircular) in the circumferential direction (indicated by dashed lines) in order to generate the desired deformations.

(15) For the machining of the running surface of the cam disc 3, the latter is pushed onto the tension tube 5, which is formed cylindrically on the outer circumference, wherein aids, such as gauges or stops, can optionally be provided (not illustrated), by means of which the cam disc 3 is positioned in a specific manner on the tension tube 5.

(16) The tension tube 5 is subsequently acted upon with high hydraulic pressure P through the fastening flange 6 and is accordingly expanded in the elastic deformation range, wherein the tension tube 5 is designed in such a manner that an outwardly directed material stress or microscopic deformation, as will also arise during the subsequent shrinking of the cam disc 3 onto the shaft 2, is exerted on the cam disc 3. By means of the hydraulic pressure, the tension tube 5 is therefore expanded, in particular expanded elastically, at least in the region assigned to the cam-disc recess 3a of the at least one cam disc 3 in such a manner that said tension tube exerts a defined tension force on the recess wall region 3b, which bounds the cam-disc recess 3a, of the cam disc 3, said tension force corresponding to a predetermined extent, preferably approximately precisely, to the state of stresses and/or deformation state of the recess wall region 3b after the operation of shrinking the cam disc 3 onto the corresponding shaft 2.

(17) FIG. 4 shows, in greatly exaggerated form, the prestressing state of the tension tube 5 against the cam disc 3; of course, said prestressing state cannot be determined simply with the eye.

(18) In said prestressing state, the cam disc 3 is fastened frictionally on the tension tube and the running surface of said cam disc can be finished or ground on the machining station, wherein the microdeformations occurring because of the subsequent shrinking of the cam disc 3 onto the shaft 2 have already been taken into consideration.

(19) After the shrinking-on operation, the structurally desired running-surface geometry and quality is already present, and therefore no remachining is required.

(20) As further shown in FIG. 4, holding aids 13 such as stops, are used to position the cam disc prior to clamping.

(21) FIG. 5 shows an alternative clamping device 8 to FIG. 4, which is described only to the extent that it differs substantially from the clamping device 4. Functionally identical parts are provided with the same reference numbers.

(22) According to FIG. 5, the tension tube 9 is expandable mechanically in the elastic deformation range, wherein, for this purpose, a pull rod 10 and a push rod 11 project through the fastening flange 6 into the tension tube 9.

(23) The pull rod 10 bears a male cone 10a in the clamping region for the cam disc 3 and is guided in the coaxial push rod 11 which is of tubular design and, as is apparent, likewise bears a male cone 11a positioned opposite to said male cone 10a.

(24) The male cones 10a, 11a interact with female cones 9a, 9b, which are formed in the tension tube 9, in such a manner that, by means of oppositely directed action of the male cones 10a, 11a via the pull rod 10 and the push rod 11 with a force F or −F, the tension tube 9 is expanded in a specific manner, as previously described.

(25) The relatively high force F can be applied via the machining station hydraulically (piston-cylinder unit) or mechanically, for example via an eccentric unit, and forms an internal force. For example, the pull rod 10 can be connected to a hydraulic piston and the push rod 11 can be connected to the cylinder of the unit, or vice versa.

(26) The machining sequence is as described with respect to FIG. 4 and likewise permits finishing of the cam disc 3 which accordingly does not require any remachining after the cam disc 3 has been shrunk onto the shaft 2.

(27) The tension tube 5 or 9 can be designed in such a manner that a plurality of cam discs 3 can be machined simultaneously in the machining device. Furthermore, a heating device 14 can optionally be provided (shown schematically in FIG. 4), said heating device, by means of temporary heating of the tension tube 5 or 9, assisting the specific expansion thereof.

(28) The assembled camshafts 1 can preferably be used for controlling the valves of internal combustion engines for motor vehicles, in particular commercial vehicles; however other camshafts can also be correspondingly designed, for example for fuel injection pumps, etc.

LIST OF REFERENCE NUMBERS

(29) 1 Camshaft 2 Shaft 3 Cam disc 3a Cam-disc recess 3b Recess wall region 4 Clamping device 5 Tension tube 5a End side 6 Fastening flange 7 Pressure connection 8 Clamping device 9 Tension tube 9a Female cone 9b Female cone 10 Push rod 10a Male cone 11 Pull rod 11a Male cone 13 Holding aid 14 Heating device