Method and device for work-hardening a crankshaft

Abstract

The invention relates to a method for work-hardening a crankshaft (4) comprising connecting rod journals (5), main bearing journals (6) and crank webs (7), the connecting rod journals (5) and the main bearing journals (6) being provided with oil holes (31). According to the invention, at least one end (30) of one of the oil holes (31) and/or at least one cylindrical portion (38) of the oil holes (31) is/are work-hardened.

Claims

1. A method for the work hardening of a crankshaft which has connecting-rod bearing journals, main bearing journals and crank webs, wherein the connecting-rod bearing journals and the main bearing journals have oil bores, wherein the oil bore end has a bevel and/or has a transition radius at the transition to a running surface of the respective journal, wherein the transition radius and/or the bevel of at least one oil bore end of one of the oil bores of a respective journal is work-hardened by an impact force being introduced into the oil bore end by an impact head having a shaping portion whose shape is adapted to the transition radius to be hardened and/or to the bevel of the oil bore end, wherein an impact tool comprises the impact head whose shape is adapted to the transition radius to be hardened and/or to the bevel of the oil bore end, wherein, the impact tool comprises at least two impact heads, each impact head of the at least two impact heads having a different diameter for the impact hardening of the oil bore end, and the impact heads of the at least two impact heads of the impact tool penetrate to different depths into the oil bore end during the impact hardening and wherein a changeover device exchanges the impact heads of the at least two impact heads of the impact tool.

2. The method as claimed in claim 1, wherein the impact tool further comprising at least two impact heads that are arranged to harden two oil bore ends which are arranged axially offset along a main axis of rotation of the crankshaft.

3. The method as claimed in claim 1, wherein a main body of the impact tool is supported by two support elements between two crank webs that surround the bearing journal that has the oil bore that is to be impact-hardened.

4. The method as claimed in claim 1, wherein at least one impact head of the impact tool for the impact hardening has a spherical surface.

5. The method as claimed in claim 1, wherein, during the impact hardening of one of the oil bore ends, a transition radius of the oil bore end or a countersink of the oil bore end is generated by at least one impact head of the impact tool.

6. The method as claimed in claim 1, wherein multiple oil bore ends of the connecting-rod bearing journals and/or of the main bearing journals are work-hardened.

7. The method as claimed in claim 1, wherein, for the impact hardening of one of the oil bore ends of the oil bores, the crankshaft is firstly rotated by a drive device along a direction of rotation into an impact position, following which an arresting device is used in order to arrest the crankshaft in the impact position, following which the impact force is introduced into the oil bore end of the oil bores by the impact tool.

8. The method as claimed in claim 1, wherein the impact tool is introduced with at least one impact head into the oil bore, following which, for the work hardening of the oil bore end, the at least one impact head is pushed radially out of the impact tool and against an internal wall of the oil bore end.

9. The method as claimed in claim 8, wherein the at least one impact head is pushed radially out of the impact tool hydraulically.

10. The method as claimed in claim 8, further comprising mechanically pushing the at least one impact head out of the impact tool using at least one wedge.

11. The method as claimed in claim 8, further comprising pneumatically pushing the at least one impact head radially out of the impact tool.

12. The method as claimed in claim 8, further comprising electromechanically pushing the at least one impact head radially out of the impact tool.

13. The method as claimed in claim 8, further comprising mechanically pushing the at least one impact head radially out of the impact tool using at least one ball screw drive.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Exemplary embodiments of the invention will be described in more detail below on the basis of the drawing.

(2) The figures each show preferred exemplary embodiments, in which individual features of the present invention are illustrated in combination with one another. Features of an exemplary embodiment are also implementable separately from the other features of the same exemplary embodiment, and may accordingly be readily combined by a person skilled in the art with features of other exemplary embodiments in order to form further meaningful combinations and sub-combinations.

(3) In the figures, functionally identical elements are denoted by the same reference designations.

(4) In the figures, in each case schematically:

(5) FIG. 1 shows an overall view of an apparatus according to the invention for carrying out the method in a first embodiment;

(6) FIG. 2 shows an exemplary flow diagram of the method according to the invention;

(7) FIG. 3 shows a perspective view of a part of the apparatus according to the invention for carrying out the method in a second embodiment;

(8) FIG. 4 shows an impact device with an impact tool and an impact head with spherical surface in an enlarged illustration as per detail “A” from FIG. 1;

(9) FIG. 5a shows an impact device with an impact tool with two impact heads, each with spherical surface, during the hardening of straight-running oil bores;

(10) FIG. 5b shows the impact device of FIG. 5a during the hardening of obliquely running oil bores;

(11) FIG. 6 shows a detail of a crankshaft with exemplary oil bores and with a connecting bore between a perpendicularly running oil bore of a connecting-rod bearing journal and a perpendicularly running oil bore of a main bearing journal;

(12) FIG. 7 shows an exemplary oil bore end of an oil bore and a schematic illustration of the impact hardening using impact heads of different size;

(13) FIG. 8 shows an example of impact hardening using an impact head which has a shaping portion;

(14) FIG. 9 shows an example of impact hardening using an impact head, wherein a transition radius or a countersink is simultaneously introduced into the oil bore end by the impact head;

(15) FIG. 10 shows an obliquely inclined impact tool in a further embodiment for the hardening of an obliquely running oil bore;

(16) FIG. 11 shows an oil bore in a sectional illustration with a transition radius, a bevel and a cylindrical portion;

(17) FIG. 12 shows a pneumatic/hydraulic or electromechanical impact tool for the work hardening of a cylindrical portion of an oil bore;

(18) FIG. 13 shows a pneumatic/hydraulic or electromechanical impact tool for the work hardening of a cylindrical portion of an oil bore with impact heads arranged in multiple height planes; and

(19) FIG. 14 shows an impact tool for the work hardening of a cylindrical portion of an oil bore by means of a wedge and multiple impact heads.

DETAILED DESCRIPTION OF THE INVENTION

(20) The apparatus illustrated in an overall view in FIG. 1 basically corresponds in terms of its construction to the apparatuses as per DE 34 38 742 C2 and EP 1 716 260 B1 with an impact device 1, for which reason only the important parts, and the differences in relation to the prior art, will be discussed in more detail below.

(21) In the exemplary embodiment, the method according to the invention for work hardening will be illustrated on the basis of an impact hardening process. This is however not to be understood as restrictive. The method according to the invention may also be realized using some other work hardening process.

(22) The apparatus has a machine bed 2 and a drive device 3. The drive device 3 is used to move or rotate a crankshaft 4 along a direction of rotation into an impact position.

(23) The crankshaft 4 has connecting-rod bearing journals 5 and main bearing journals 6, between which crank webs 7 are arranged in each case. Transition radii 8 (see FIGS. 4 to 6) are formed between connecting-rod bearing journals 5 and crank web 7 and between main bearing journals 6 and crank web 7, or generally between transitions in cross section of the crankshaft 4.

(24) At that side of the crankshaft 4 which faces toward the drive device 3, there is provided a fastening device 9 which has a clamping disk or a fastening flange 10. On that side of the crankshaft 4 which is averted from the drive device 3, a support 11 preferably in the manner of a tailstock is provided, which has a further fastening device 9 for the purposes of rotatably receiving or rotatably fixing the crankshaft 4. Optionally or in addition to the support 11, a back rest may be provided which is positioned at a rotationally symmetrical location.

(25) In accordance with one embodiment of the invention, an arresting device 12 is provided, which engages in the region of an outer circumference of the fastening device 9. Basically, the arresting device 12 may be arranged at any desired location within the apparatus in order to apply an arresting force to an output shaft of the drive device 3, or to an input shaft 13, which in the present case is identical to said output shaft, of the fastening device 9, and thus to the crankshaft 4. The arresting device 12 may also engage on multiple locations of the apparatus. By way of example, a second part of the arresting device 12 in engagement with the fastening device 9 in the region of the support 11 is illustrated by dashed lines.

(26) The arresting device 12 is based for example on a non-positive arresting action using a merely schematically illustrated brake shoe arrangement 14.

(27) The impact device 1 illustrated in FIG. 1 is an impact device 1 for the impact hardening of at least one oil bore end 30 (see in particular FIG. 7 to FIG. 9) of an oil bore 31 (see FIG. 4 to FIG. 10) and/or of at least one cylindrical portion 38 (see FIG. 11) of one of the oil bores 31. The illustrated impact device 1 may however also be designed for the impact hardening of at least one transition radius 8 between a connecting-rod bearing journal 5 and a crank web 7 and/or at least one transition radius 8 between a main bearing journal 6 and a crank web 7 of a crankshaft 4. It is also possible for multiple impact devices 1 to be provided, wherein at least one of the impact devices 1 is designed for hardening the oil bore ends 30 and/or the cylindrical portion 38 and at least one further impact device is designed for hardening the transition radii 8 between connecting-rod bearing journals 5 and crank web 7 and/or between main bearing journals 6 and crank web 7.

(28) For the functional principle of the invention, an arresting device 12 is basically not necessary but may be advantageous, for example also for the impact hardening of obliquely running oil bores 31 in order to prevent rotation of the crankshaft 4 during the introduction of the impact force.

(29) FIG. 1 furthermore illustrates a displacement and adjustment device 15 which is provided for moving the impact device, which is illustrated by way of example, along the longitudinal axis of the crankshaft in order to correspondingly position the impact device 1 at the connecting-rod bearing journal 5 or the main bearing journal 6 whose oil bore or oil bore end is to be impact-hardened.

(30) FIG. 2 shows an exemplary flow diagram for an exemplary method which may be composed of four steps (rotating, arresting, impacting, releasing). The method steps of arresting and of releasing are in the present case optional but advantageous.

(31) For the operation of the drive device 3, which preferably comprises an electric motor, closed-loop position control may be used in order to rotate the crankshaft 4 into the respective impact position, wherein the crankshaft 4 is rotated preferably in stepped or clocked fashion.

(32) After the crankshaft 4 has been rotated by the drive device 3 into the impact position, the crankshaft 4 is initially arrested in the impact position by the optional arresting device 12.

(33) Subsequently, by means of at least one impact tool 16 (see FIG. 4, FIGS. 5a/5b and FIG. 10), an impact force is introduced into at least one oil bore end 30 of an oil bore 31 of the crankshaft 4 and/or into at least one cylindrical portion 38 of an oil bore 31 of the crankshaft 4. Additionally, an impact force may also be introduced into at least one transition radius 8 of the crankshaft 4 by means of the same or at least one (further) impact tool.

(34) Preferably, the controller of the drive device 3 and the controller of the arresting device 12 are synchronized with one another such that the arresting device 12 arrests the crankshaft 4 only when the crankshaft 4 is at a standstill in the impact position.

(35) Furthermore, it is also possible for the controllers of the arresting device 12 and of the at least one impact tool 16 (or of the at least one impact device 1) to be synchronized such that the at least one impact tool 16 introduces the impact force into the oil bore end 30 or into the cylindrical portion 38 of the crankshaft 4 only when the crankshaft 4 has been arrested in the impact position. The arresting of the crankshaft 4 is subsequently released again.

(36) The method may subsequently be repeated as often as desired for the same oil bore end 30 or the same oil bore 31, for example also through slight modification of the impact position and/or of the impact angle.

(37) After an oil bore end 30 and/or a cylindrical portion 38 has been impact-hardened in the desired manner, the impact tool 16 or the entire impact device 1 can be moved to the next oil bore end 30 to be hardened and/or to the next cylindrical portion 38 to be hardened (of the same or another oil bore 31), following which the method comprising the steps “rotating”, “arresting” (optional), “impacting” and “releasing” (optional) can be repeated.

(38) Similarly, a controller or a sequence for the impact hardening of transition radii 8 between connecting-rod bearing journals 5 and crank webs 7 and/or between main bearing journals 6 and crank webs 7 may be provided. A common controller may also be provided.

(39) The at least one impact tool 16 or the at least one impact device 1 may introduce the impact movement or the impact force with a periodicity, for example with a timing and/or impact frequency of 0.1 Hz to 50 Hz, preferably with a timing and/or impact frequency of 0.3 Hz to 10 Hz, particularly preferably with a timing and/or impact frequency of 0.5 Hz to 5 Hz and very particularly preferably with a timing and/or impact frequency of 0.5 Hz to 3 Hz. Provision may be made here whereby multiple (at least two) impacts are introduced into an oil bore 31 with the stated impact frequency or, in the case of the hardening of transition radii 8 between connecting-rod bearing journals 5 and crank webs 7 or transition radii 8 between main bearing journals 6 and crank webs 7, the impact position is changed with the stated timing, following which in each case one or more impacts are performed.

(40) An open-loop and/or closed-loop control device 29, preferably comprising a microprocessor, may be provided for carrying out the method. The open-loop and/or closed-loop control device 29 may for example also comprise or implement and/or synchronize the controllers of the drive device 3, of the arresting device 12 and/or of the at least one impact tool 16.

(41) In particular, a computer program with program code means may be provided in order to carry out the method according to the invention when the program is executed on an open-loop and/or closed-loop control device 29, in particular on a microprocessor.

(42) FIG. 3 illustrates, in a perspective view, a detail of a further apparatus for carrying out the method according to the invention—but without an impact device. Here, the apparatus of FIG. 3 is substantially identical to the apparatus of FIG. 1, for which reason only the important differences will be referred to below.

(43) A drive device 3 is once again provided. In the embodiment of FIG. 3, it is furthermore the case that an optional arresting device (not visible) is also arranged within the drive device 3. Although the arresting device is preferably arranged as illustrated in FIG. 1, the arresting device may thus also be accommodated within the drive device 3. Provision is however nevertheless made here whereby the arresting device is activatable separately from the drive device 3. In FIG. 3, the arresting device is not a constituent part of the drive device 3. The drive device 3 may possibly additionally have a dedicated brake device.

(44) Furthermore, a fastening device 9 is provided which has a fastening flange 10 and, fastened thereto, a face plate with clamping jaws for fixing the crankshaft 4. The face plate with the clamping jaws of the fastening device 9 is arranged on the fastening flange 10 adjustably on an alignment means 17, whereby the longitudinal axis C.sub.KW of the crankshaft 4 can be displaced relative to the axis of rotation C of the drive shaft 13.

(45) The crankshaft 4 of FIG. 3 has a configuration which deviates from the crankshaft 4 of FIG. 1, but basically likewise comprises connecting-rod bearing journals 5, main bearing journals 6 and crank webs 7.

(46) In FIG. 3 (as in FIG. 1, too), a further fastening device 9 may be provided at that end of the crankshaft 4 which is averted from the drive device 3, though said further fastening device may also be omitted.

(47) An impact device 1 of FIG. 1 is illustrated in more detail by way of example in FIG. 4. The method for impact hardening may basically be implemented using any impact device 1. The impact device 1 described below is however particularly suitable. It has a main body 18 which may be provided with a prismatic abutment corresponding to the radius of the crankshaft segment to be machined, and which preferably has guides 19 which guide an impact tool 16 and provide it with a corresponding degree of freedom in terms of the support angle about a deflection unit 20, which is advantageous for the adaptation to the dimensional conditions of the crankshaft 4. A ball as impact head 21 is arranged at the front end of the impact tool 16, that is to say the impact head 21 has a spherical surface for the impact hardening. An intermediate part 22 produces the connection between an impact piston 23 and the deflection unit 20, which transmits the impact energy to the impact tool 16. The intermediate part 22 may possibly also be omitted.

(48) To increase the effectiveness of the impact, a clamping prism 24 may be fastened, via springs, by means of adjustable clamping bolts with clamping nuts to that side of the journal 5 which is averted from the main body 18 (not illustrated in detail here). Other structural solutions are also possible here.

(49) By means of the arrangement of multiple impact devices 1 over the length of the crankshaft 4 to be machined, it is possible, as required, for several to all regions or oil bores 31 of the crankshaft 4 to be machined simultaneously.

(50) In the crankshaft 4 illustrated in FIG. 4, an oil bore 31 is illustrated by dashed lines in the connecting-rod bearing journal 5, which oil bore runs centrally and perpendicularly in the connecting-rod bearing journal 5 and ends approximately in the middle of the connecting-rod bearing journal 5. A connecting bore 32 is provided for the connection to the oil circuit of the engine block via an adjoining main bearing journal 6. The connecting bore 32 leads to an oil bore (not illustrated in FIG. 4) of a main bearing journal 6. The impact device 1 and the impact tool 16 are, in the exemplary embodiment, aligned such that an oil bore end 30 of the oil bore 31 can be impact-hardened. For this purpose, the impact force is introduced into the oil bore end 30 by means of the impact head 21 of the impact tool 16.

(51) For the alignment of the impact tool 16 with the oil bore end 30, the main body 18 of the impact device 1 is supported by two support elements 33 (or a multi-part or encircling support element) on the crank webs 7 that adjoin the connecting-rod bearing journals 5. The support elements 33 may also serve to ensure that the impact tool 16 does not buckle or slip during the impact hardening of the oil bore end 30.

(52) It is basically possible for multiple, preferably a majority of, particularly preferably all, oil bore ends 30 of the connecting-rod bearing journals 5 and/or of the main bearing journals 6 to be work-hardened or impact-hardened. It is preferable for all oil bore ends 30 of all connecting-rod bearing journals 5 to be impact-hardened.

(53) FIGS. 5a/5b illustrate a further impact device 1 which has an impact tool 16 on which two impact heads 21 are arranged in order to harden two oil bore ends 30 which are arranged axially offset along the main axis of rotation C.sub.KW of the crankshaft 4, or axis of rotation C, in the same journal 5, 6.

(54) Here, the impact device 1 of FIGS. 5a/5b is basically of similar construction to the impact device 1 of FIG. 4, and is likewise illustrated merely schematically. The impact device 1 of FIGS. 5a/5b likewise has a deflecting unit 20 in order to distribute the impact force generated by the impact piston 23 between the impact heads 21 via an intermediate part 22. At the same time, the deflecting unit 20 can serve for optimally aligning the impact tool 16 with the oil bore ends 30. For support, it is once again possible for one or more support elements 33 or an encircling support element to be provided, which in the present case are arranged between the impact tool 16 and the corresponding crank webs 7.

(55) An impact device 1 may basically be used for the impact hardening of straight-running oil bores 31 (see FIG. 5a) or for the impact hardening of obliquely running oil bores 31 (see FIG. 5b). This self-evidently also applies if only one impact tool 16 and/or one impact head 21 and/or one oil bore 31 in one journal 5, 6 is to be hardened.

(56) Provision may also be made whereby, for the work hardening of an oil bore 31 or of an oil bore end 30, a spherical body 34 is pushed through at least one portion of the oil bore 31. This is schematically illustrated in FIG. 6.

(57) Here, provision may be made whereby the spherical body 34 is pushed in pulsed fashion or uniformly into the at least one portion of the oil bore 31. The spherical body 34 may also be an impact head 21 as already described. The spherical body 34 is preferably removed from the oil bore 31 again after the hardening of the internal walls of the oil bore 31.

(58) FIG. 6 shows an exemplary detail of a crankshaft 4 with in each case one oil bore 31 in a connecting-rod bearing journal 5 and a main bearing journal 6. A connecting bore 32 is formed between the two illustrated oil bores 31. During the later operation of the crankshaft 4, provision may then be made for the mouth of the connecting bore 32 at a crank web 7 to be closed using a sealing means 35 in order that the oil circuit is closed. As an alternative to this, it is also possible for one or both oil bores 31 to converge on one another obliquely.

(59) As already stated above, provision may be made for the oil bore end 30 of an oil bore 31 of the connecting-rod bearing journal 5, or the entire oil bore 31 of the connecting-rod bearing journal 5 or any cylindrical portion 38 on the inside or on the internal walls of the oil bore 31, to be hardened by virtue of the spherical body 34 being pushed through the oil bore 31. For this purpose, the spherical body 34 has a slightly larger diameter than the oil bore 31.

(60) If, owing to the application, it is necessary or advantageous for the spherical body 34 to be pushed into the oil bore 31 to such a depth that the spherical body 34 can no longer be pulled back or pulled out by the impact tool 16 or the pulling-out is considered disadvantageous, provision may be made whereby the spherical body 34 passes from the oil bore 31 of the connecting-rod bearing journal 5 directly, or via a connecting bore 32, to an oil bore 31 of an adjoining main bearing journal 6, wherein the connecting bore 32 and/or the oil bore 31 of the main bearing journal 6 have an inner diameter at least as large as the outer diameter of the spherical body 34.

(61) Thus, as soon as the spherical body 34 has been pushed into the oil bore 31 to such a depth that the spherical body 34 arrives at the connecting bore 32, which has a larger diameter than the spherical body 34 and the oil bore 31 of the connecting-rod bearing journal 5, the spherical body 34 can pass, for example roll, through the connecting bore 32 to the oil bore 31 of the main bearing journal 6, from where the spherical body can be removed from the crankshaft 4 again if the oil bore 31 of the main bearing journal 6 also has a larger diameter than the spherical body 34.

(62) FIG. 7 shows an enlarged illustration of an oil bore end 30. At the transition to the running surface 36 of the corresponding journal 5, 6, the oil bore end 30 has a transition radius R which is impact-hardened. Instead of a transition radius R, the oil bore end 30 at the transition to the running surface 36 may also have any desired countersink. The oil bore end 30 may however also be provided without a transition radius R or a countersink. Provision may also be made whereby the oil bore end 30 has a transition radius R and a bevel 39, as illustrated in FIG. 11.

(63) An oil bore end 30 of the oil bore 31 is also illustrated in FIG. 7. The oil bore end 30 may basically comprise only the mouth of the oil bore 31, that is to say for example the transition radius R and/or the bevel 39 (see FIG. 8 and FIG. 11). Provision may however also be made whereby the oil bore end 30 that is to be work-hardened projects into the oil bore 31 to a depth T. The depth T may be determined by simulations, calculations and/or series of tests of the respective crankshaft type.

(64) Provision may be made whereby, for the impact hardening of the oil bore end 30, use is made of impact heads 21 with different diameters, in such a way that the impact heads 21 penetrate to different depths into the oil bore end 30 during the impact hardening.

(65) For example, a changeover device 37 (merely schematically illustrated) may be provided for the purposes of selecting and/or changing over the impact heads 21. In the exemplary embodiment of FIG. 7, it is indicated in this regard that the changeover device 37 exchanges the impact tool 16 in order to change over the impact heads 21. Provision may however also be made for the changeover device 37 to directly change over the impact heads 21 or to change over the entire impact device 1.

(66) Also illustrated in FIG. 7 is an impact head 21, which, as a spherical body 34, can be pushed through the oil bore 31. For this purpose, the impact tool 16 may for example be designed to eject the impact head 21 or the spherical body 34 after or during the pushing-in process. The internal walls of the oil bore 31 are preferably work-hardened at least as far as the depth T or extent of the oil bore end 30. The diameter of the spherical body 34 is selected, for the work hardening of the internal walls of the oil bore 31, larger than or equal to the diameter D of the oil bore 31.

(67) Finally, FIG. 8 shows a further oil bore end 30, which comprises only the transition radius R of the oil bore 31. For the impact hardening, an impact head 21 is used which has a shaping portion whose shape is adapted to the transition radius R, which is to be hardened, of the oil bore end 30.

(68) It is also possible for a countersink or a bevel 39 and/or a transition radius R of an oil bore end 30 to be generated in the first place by means of a shape-imparting impact tool 16 or a corresponding impact head 21 as a result of the impact hardening. Such a plastic deformation by means of an impact head 21 is shown in FIG. 9, wherein a round or symmetrical impact head 21 is indicated; this may however also be a non-symmetrical impact head 21 (any spherical cap). Any desired countersink can be generated through the selection of a corresponding impact head 21, for example also of an impact head 21 which has a shaping portion.

(69) Finally, FIG. 10 shows a further impact device 1 which is equipped with only one impact tool 16. In the exemplary embodiment shown, the impact device 1 is not orthogonal but rather inclined obliquely with respect to the central axis or main axis of rotation C.sub.KW of the crankshaft 4, specifically such that the central axis or longitudinal axis L.sub.S of the impact tool 16 is aligned coaxially with respect to the central axis of the oil bore 31 in order to introduce the impact force along the central axis of the oil bore 31.

(70) FIG. 11 shows a further oil bore 31 within a journal 5, 6 of a crankshaft 4 for the purposes of illustrating the terminology. The oil bore 31 illustrated in FIG. 11 has a transition radius R at the transition to the running surface 36 of the journal 5, 6, which transition radius is adjoined by a bevel 39. In the exemplary embodiment of FIG. 11, the oil bore mouth 30 is defined as extending from the transition radius R to the depth T, and accordingly also comprises an upper cylindrical portion 43 of the oil bore 31. According to the invention, provision may be made for the oil bore mouth 30 to be work-hardened as far as a depth T, that is to say for the transition radius R, the bevel 39 and the upper cylinder portion 43 of the oil bore 31 to be work-hardened. In the context of the invention, it is however also possible for only the transition radius R, only the bevel 39, only the transition radius R and the bevel 39, or only the bevel 39 and the upper cylindrical portion 43 of the oil bore 31, to be work-hardened.

(71) Provision may also be made for only one or more arbitrary cylindrical portions 38 within the oil bore 31 to be work-hardened. An exemplary cylindrical portion 38 is illustrated in FIG. 11. The cylindrical portion 38 may comprise a part of any size of the cylindrical part of the oil bore 31. The cylindrical portion 38 may adjoin the bevel 39, though may also be spaced apart from the bevel 39. The cylindrical portion 38 may also be formed in multiple parts in the cylindrical part of the oil bore 31.

(72) Various impact tools 16 may be used for the hardening of a cylindrical portion 38 of an oil bore 31. Three exemplary embodiments are shown in FIGS. 12 to 14. Here, in each case, provision is made whereby the impact tool 16 is introduced with at least one impact head 21 into the oil bore 31 as far as a desired depth, following which, for the work hardening (preferably impact hardening) of the at least one cylindrical portion 38 of the oil bore 31, the at least one impact head 21 is pushed radially out of the impact tool 16 and against an internal wall 40 of the at least one cylindrical portion 38.

(73) In FIG. 12, merely for illustrative purposes, the right-hand impact head 21 is illustrated in a position bearing against the internal wall 40, whereas the left-hand impact head 21 is still situated in its initial position. The impact heads 21 are preferably pushed outward symmetrically.

(74) To secure the impact heads 21 in their initial position, corresponding shoulders etc. may be provided in the impact tool 16, as indicated in FIGS. 12 and 13.

(75) Basically any number of impact heads 21 may be provided. For example, one, two, three, four, five, six or even more impact heads 21, which are in particular arranged symmetrically around a central axis M of the impact tool 16. In the exemplary embodiment of FIG. 12, two impact heads 21 are illustrated, wherein a further impact head 21 (preferably of a further impact head pair) is indicated by way of example using dashed lines.

(76) The impact heads 21 may also be arranged at different height levels, as illustrated in FIG. 13. In this way, it is possible to machine a relatively large cylindrical portion without axial adjustment, or with relatively little axial adjustment, of the impact tool 16.

(77) Provision may additionally be made for the impact tool 16 to be rotated along the central axis of the oil bore 31 during the machining process, in order to perform the most uniform and complete possible machining of the internal surface of the oil bore 31. This is indicated in FIGS. 12 to 14 by means of corresponding arrows.

(78) Provision may be made whereby the at least one impact head 21 is pushed radially out of the impact tool 16 hydraulically, pneumatically or electromechanically. For this purpose, the impact tool 16 may have a corresponding compressed-air or liquid supply 41. Alternatively, as illustrated in FIG. 14, a mechanical adjustment of the at least one impact head 21 may be provided, for example by means of a wedge 42 or a ball screw drive (not illustrated). FIG. 14 illustrates an embodiment in which a double wedge 42 is used which simultaneously axially secures the impact heads 21. It is however also possible for only a single wedge to be provided (for example only the upper half of the double wedge 42), if the impact heads 21 are secured in some other way against falling out of the impact tool 16.