Large transmission gearwheel and process for producing a large transmission gearwheel

Abstract

The invention relates to a process for producing a large transmission gearwheel (1; 31; 36) consisting of a plurality of individual components, said process comprising the successive steps of: providing the individual components, which include at least one hub (2; 32; 37), a disc wheel (3, 4; 18, 19; 22; 24; 27; 33, 34; 38, 39) and a toothed ring (5; 20; 21; 23; 26; 35; 40) produced from case-hardened steel; at least partially mechanically soft machining the individual components; joining the individual components using a beam welding process; case hardening the individual components which have been joined to one another, and hard machining at least the toothed ring (5; 20; 21; 23; 26; 35; 40). The invention furthermore relates to a large transmission gearwheel produced by such a process.

Claims

1. A method for producing a large transmission gearwheel, comprising: at least partially mechanically soft machining individual components of a large transmission gearwheel, with the individual components involving a hub, a disk wheel of case-hardened steel, and a toothed ring; joining the individual components using a beam welding method; case hardening the joined individual components thereby producing the large transmission gearwheel having a flank strength of at least 1250 N/mm.sup.2; and directly after case hardening hard machining at least the toothed ring for configuring the disk wheel asymmetrically.

2. The method of claim 1, wherein the beam welding method is an electron beam welding method.

3. The method of claim 1, wherein the beam welding method includes laser beam welding.

4. The method of claim 3, further comprising executing the laser beam welding under vacuum or partial vacuum.

5. The method of claim 1, wherein hard machining includes hard turning and gear teeth grinding of at least the toothed ring.

6. The method of claim 1, further comprising providing the disk wheel with at least one eccentric recess.

7. The method of claim 1, further comprising providing the disk wheel with a plurality of eccentric recesses.

8. The method of claim 1, further comprising adjusting a deformation of the large transmission gearwheel by the asymmetrical configuration of the disk wheel.

9. The method of claim 1, further comprising adjusting a stiffness of the large transmission gearwheel by an asymmetrical configuration of a thickness of the toothed ring.

10. The method of claim 1, wherein the individual components involve two of said disk wheel arranged in axially spaced-apart relationship, and further comprising mounting the two disk wheels from one side relative to the toothed ring, with the soft machining of the individual components executed from said side.

11. The method of claim 1, further comprising executing the beam welding method to produce at least one weld joint, which, viewed in the welding direction, has a rear end formed by a radially protruding projection which is part of one of the individual components to be welded together by the beam welding method.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Further features and advantages of the present invention are revealed from the following description of exemplary embodiments of the present invention with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic side view of a large transmission gearwheel according to an embodiment of the present invention;

(3) FIG. 2 is a cross-sectional view along the large transmission gearwheel shown in FIG. 1 along the line II-II in FIG. 1;

(4) FIG. 3 is an enlarged view of the detail III in FIG. 2;

(5) FIG. 4 is a basic sketch which shows the tooth profile of oblique gear teeth of a toothed ring;

(6) FIG. 5 is a schematic partial cross-sectional view of a toothed ring of a large transmission gearwheel according to a second embodiment of the present invention;

(7) FIG. 6 is a diagram which shows the stiffness profile of the toothed ring shown in FIG. 5 over the width of the toothed ring;

(8) FIG. 7 is a schematic enlarged cross-sectional view of a transition between the disk wheel and the toothed, ring of a large transmission gearwheel according to a third embodiment of the present invention which shows a possible weld pool support;

(9) FIG. 8 is a schematic enlarged cross-sectional view of a transition between the disk wheel and toothed ring of a large transmission gearwheel according to a fourth embodiment of the present invention which shows a possible weld pool support;

(10) FIG. 9 is a schematic enlarged cross-sectional view of a transition between the disk wheel and toothed ring of a large transmission gearwheel according to a fifth embodiment of the present invention which shows a possible weld pool support;

(11) FIG. 10 is a schematic view of a large transmission gearwheel according to a sixth embodiment of the present invention in which the toothed ring and disk wheel are welded together radially; and

(12) FIG. 11 is a schematic side view of a large transmission gearwheel according to a seventh embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(13) FIGS. 1 to 3 show a large transmission gearwheel 1 according to an embodiment of the present invention. The large transmission gearwheel 1 is a hybrid gearwheel which is produced from a plurality of individual components and namely from a hub 2, two disk wheels 3 and 4 and a toothed ring 5, which are welded together at the positions illustrated by the arrows A.

(14) The hub 2 is configured to be substantially cylindrical and comprises a radially protruding projection 6 which extends substantially centrally along the periphery of the hub 2 and serves as a stop for positioning the disk wheels 3 and 4.

(15) The disk wheels 3 and 4 in each case are provided with recesses 7 arranged eccentrically. The recesses 7 in each case have different shapes and are distributed asymmetrically on the disk wheels 3 and 4 arranged as shown in FIG. 1.

(16) The toothed ring 5 is produced from a case-hardened steel and is case hardened. It comprises a connecting portion 8 and a toothed ring portion 9 configured in one piece therewith, which are connected together via a transition radius 10. The connecting portion is provided with two annular connecting surfaces 11 and 12 along which the toothed ring 5 is welded to the disk wheels 3 and 4. Between the connecting surfaces 11 and 12 extends a radially inwardly protruding projection 13 which serves as a stop for the disk wheels 3 and 4. The dimension a illustrated in FIG. 3 denotes the radial distance between the transition radius 10 and the connecting surfaces 11 and 12 and/or the weld seams provided there. The distance a is selected to be of such a size that the notch effect, which is produced by the weld seams provided as closed circumferential seams, is safely decoupled. The dimension b illustrated in FIG. 3 denotes the minimum ring thickness of the disk wheels 3 and 4 for producing a weld seam which is thermally acceptable along the recesses 7 provided on the disk wheels 3 and 4, in order to ensure a substantially uninterrupted and symmetrical dissipation of heat.

(17) The dimension c in FIG. 3 is the difference between the radial height of the ring projection 13 of the toothed ring 5 and the minimum ring thickness b of the disk wheels 3 and 4 which is required to form a structure through which the media used during case-hardening is able to flow and pass through, as described in more detail hereinafter.

(18) The dimensions a, b and c are selected in accordance with the structure based on a corresponding calculation.

(19) The large transmission gearwheel 1 shown in FIGS. 1 to 3, according to an embodiment of a method according to the invention is produced as follows. In a first step, the individual components are produced, i.e. the hub 2, the two disk wheels 3 and 4 and the toothed ring 5. In a further step a mechanical soft machining is carried out on the individual components. In this case, the hub 2 is subjected to a turning operation. Subsequently, the toothed ring 5 is provided with its gear teeth, which may be carried out for example during the course of a hobbing treatment. Subsequently, the disk wheels 3 and 4 are inserted and/or pressed between the hub 2 and the toothed ring 5. Simple interference fits of the disk wheels 3 and 4 should be used here. The radii in the projections of the contact surfaces for the disks in the region of the radial and axial stop surfaces have to be considered according to the internal chamfer of the disk to be inserted. The disks also advantageously have a larger radius internally than on the external side where the welding will take place. The preparation of the weld seam should, however, be implemented by considering costs and avoiding unnecessary projecting portions. In a further step the individual components are then connected together at the positions identified by the arrows A by using a beam welding method, wherein the beam welding method is preferably an electron beam welding method. Alternatively, a laser beam welding method under vacuum or partial vacuum may also be used.

(20) Subsequently, the large transmission gearwheel 1 is case hardened in the welded state, whereby the toothed ring 5 obtains a flank strength of 1250 N/mm.sup.2, preferably 1500 N/mm.sup.2 or more. This is followed by a hard machining process, the grinding of at least the toothed ring 5 being carried out during the course of this hard machining process. However, a hard machining of the hub 2 and/or the disk wheels 3 and 4 may also be carried out, for example, during the course of a hard turning process.

(21) A substantial advantage of the described method is that during the beam welding of the individual components only a small amount of heat is introduced into the component which results in relatively small residual stresses caused by the welding method in comparison with the conventionally used welding methods using consumable electrodes. Accordingly, these may be dissipated by the thermal treatment taking place during the case hardening (stress relief tempering). By the corresponding choice of the dimension a, i.e. the distance of the transition radii 10 from the weld seams and/or connecting surfaces 11 and 12, the notch effect is also decoupled. Due to the case hardening a very high flank strength is provided to the toothed ring 5, so that the large transmission gearwheel 1 is able to withstand the highest loads. The unavoidable component deformation during the case hardening is minimized by the corresponding choice of shape and position of the recesses 7. These recesses 7 ensure effective penetration of carbonizing gases during the carbonizing. Moreover, the quenching means are distributed uniformly during the quenching process, such that the temperature distribution is as uniform as possible in the individual regions of the large transmission gearwheel 1 during cooling and/or quenching, effectively counteracting component deformation due to local temperature differences. Moreover, the ability to clean the large transmission gearwheel 1 is also improved by means of the recesses 7. It should be clear that the recesses 7 may also be configured and arranged differently. For example, a symmetrical arrangement of circular recesses 7 may also be selected if this results in a component having low deformation.

(22) A further advantage of the method according to the invention is that the hard machining may be carried out at relatively low cost due to the low component deformation during the aforementioned method steps, which is why the costs for the hard machining are relatively small.

(23) It should be clear that further steps for quality control may be associated with the previously described method steps. Moreover, reference should be made to the fact that the large transmission gearwheel 1 may also have only one individual disk wheel.

(24) FIG. 4 shows schematically the tooth profile 14 of oblique gear teeth of a toothed ring 15 in plan view and in side view. The driving gearwheel 15 moves during the operation with the sharper tooth edge 16 into the driven wheel (not shown). In principle, this tooth edge 16 is less stiff than the opposing tooth edge 17 which has an obtuse angle. The contact pattern of the oblique gear teeth moves with increasing load from the tooth edge 16 to the tooth edge 17 and is optimized according to a specific topographical correction in the contact pattern.

(25) The load-bearing behavior of gearwheels is, in particular in the case of high-strength, case-hardened gearwheel materials which permit a high load carrying capacity, superimposed by a noticeable deformation of the resilient transmission parts and components. In addition, the flexion at the tooth tips is generally many times greater than the shape deviations on the tooth as a result of the production process. The loading also causes deflections and twisting of the pinion shaft and gearwheel shaft, pinion body and disk wheel body and lowering of the bearings and housing deformations. This results in misalignments of the tooth flanks which are frequently considerably greater than the flank line deviations as a result of the production process. This results in a non-uniform bearing of the gear teeth surface in height and width, which influences both the load-bearing capacity and the noise behavior.

(26) In order to reproduce the high load-bearing capacity of high-strength gearwheels and to reduce greater noise development, specific deviations from the involute (height modification) and the theoretical flank line (width modification) are made in order to obtain almost ideal geometries with uniform load distribution under load.

(27) When determining the height and width modifications the entire area of influence of the substructure has to be taken into account. The deformation chain via the gearwheel, the shaft, the bearing, the housing and the housing connection to the main shaft has to be considered. By modifying the height at the tooth tip or at the tooth root and by modifying the flanks or width, the involute is superimposed by a correction shape which is intended to permit a uniform bearing of the teeth and the dissipation of the load concentrations at the tooth ends during axial displacements. These influences are calculated on the individual components and then added together and transferred as an interface to the adjacent gear teeth layout and also have to take into account the respective joints of the welded large transmission gearwheels. In particular, the shaft deformation, the bearing deformation, the production tolerances which have to be considered, the deformation of the gear teeth and the deformation of the joined disk wheels have to be allowed for. Thus a further problem is to consider specifically the deformation of the welded large transmission gearwheel with highly loaded gearwheels.

(28) FIGS. 5 and 6 show a variant in the stiffness which is able to be produced according to the invention. Due to an increase in the thickness of the toothed ring on one side, according to the invention the stiffness may be manipulated for embedding the toothed ring. This may be associated with both the driving wheel and for the driven wheel, so that a superimposition takes place with the correction shape of the gear teeth for a more uniform load-bearing behavior over a wider loading range. FIG. 5 shows a toothed ring 20 welded to the disk wheels 18 and 19, which is the toothed wheel 15 of the driving wheel in the modified state shown in FIG. 4. An advantage of this modification according to the invention is that the edge regions of the gear teeth of the toothed ring 20 due to locally reduced thickness of the toothed ring are supported in a less rigid manner in order to avoid corner supports, i.e. excessive and damaging support only via the edges. Moreover, the interfaces between the disk wheels 18 and 19 and the toothed ring 20 are easily accessible by reducing the thickness of the toothed ring on the radial internal edge regions of the toothed ring 20, whereby a positive weld beam coupling is permitted in the direction of the arrows A. A further positive effect is that the turning machining of the toothed ring 20 is possible on one side during the soft machining process, whereby costly clamping on both sides of the component is avoided.

(29) FIGS. 7 and 9 show schematic enlarged cross-sectional views of transitions between the disk wheel and the toothed ring of a large transmission gearwheel according to different embodiments of the present invention, which show possible variants of weld pool supports.

(30) FIG. 7 shows a toothed ring 21 which is welded to a disk wheel 22. To achieve an inner weld pool support the disk wheel 22 is provided at its rear endviewed in the welding direction (arrow A)along its outer periphery with a peripheral radially outwardly protruding projection 22a which engages in a correspondingly configured recess which is configured on the periphery at the rear end of the inner periphery of the toothed ring 21.

(31) FIG. 8 shows a toothed ring 23 which is welded to a disk wheel 24, wherein the width of the disk wheel is selected to be larger than the width of the toothed ring 23. To achieve an outer weld pool support the disk wheel 24 is provided at its rear endviewed in the welding direction (arrow A)along its outer periphery with a radial outwardly protruding projection 24a which encompasses the toothed ring 23 at the rear.

(32) FIG. 9 shows a toothed ring 26 which is welded to a disk wheel 27. The disk wheel 27 is provided along its outer periphery with a projection 28 protruding axially on both sides, at the rear end thereofviewed in the welding direction (arrow A)a peripheral radially outwardly protruding projection 28a being configured which encompasses the toothed ring 26 to the rear. The toothed ring 26 is also provided along its internal periphery with a projection 30 protruding axially to the front (counter to the welding direction) which is substantially aligned in the radial direction with the projection 28 of the disk wheel 27. After welding the toothed ring 26 and the disk wheel 27, the projections 28 and 30 may be machined down so that the toothed ring 27 and the disk wheel 26 merge with one another in an aligned manner.

(33) FIG. 10 is a schematic view of a hybrid large transmission gearwheel 31 according to a further embodiment of the present invention, which also is produced from a hub 32, two disk wheels 33 and 34 and a toothed ring 35. Whilst the hub 32 is welded to the disk wheels 33 and 34 in the axial direction, as in the previous embodiments, the disk wheels 33 and 34 are welded to the toothed ring 35 in this embodiment in the radial direction. It should be clear that for the weld seams weld pool supports are also provided by a corresponding design of the hub 32, the disk wheels 33 and 34 and the toothed ring 35, even if this is not shown in the schematic illustration according to FIG. 10.

(34) FIG. 11 shows a schematic side view of a large transmission gearwheel 36 according to a further embodiment of the present invention. The large transmission gearwheel 36 is also a hybrid gearwheel which consists of a hub 37, two disk wheels 38 and 39, and a toothed ring 40 which are welded together. The design of the large transmission gearwheel 36 substantially corresponds to that of the large transmission gearwheel 1 shown in FIGS. 1 to 3. In contrast to the large transmission gearwheel 1, however, the recesses 41 are symmetrically arranged in the gearwheel 31 and have a circular shape. Moreover, axially extending tubular strips 42 which connect the disk wheels 38 and 39 together are provided, whereby the structure is additionally reinforced. In other respects, the structures of the large transmission gearwheels 1 and 36 correspond to one another.

(35) Although the invention in detail has been illustrated and described more specifically by the preferred exemplary embodiment, the invention is not limited by the disclosed examples and other variants may be derived therefrom by the person skilled in the art, without departing from the protected scope of the invention.