GB2111884A - A device for eliminating deformations and/or denting of the teeth of a gear wheel - Google Patents

Abstract

A device operable to eliminate deformations and/or dents in the teeth of a gear wheel (2), comprises a tool (13) operable to mesh with the said gear wheel (2), means (11) for pressing the said tool (13) and the said gear wheel (2) together at a constant pressure, and a control member (8) operable to transmit rotary movement to the said gear wheel (2) or to the said tool (13); the said gear wheel (2) and the said tool (13) having respective axes which are skew with respect to one another. <IMAGE>

Description

SPECIFICATION A device for eliminating deformations and/or denting of the teeth of a gear wheel, particularly in a phase subsequent to one in which a heat treatment has been performed The present invention relates to a device for eliminating deformations and/or denting of the teeth of a gear wheel, particularly in a phase subsequent to one in which a heat treatment has been performed.

As is known, in the cycle of operations for making gear wheels by mass production or medium production runs there occur problems of errors which cause gear coupling noise. Before effecting the heat treatment, and therefore when the gear wheel is of relatively soft steel, the teeth are first formed and then a trimming operation is performed with a steel tool of super-rapid type which finishes the gear wheel with very narrow tolerances. During the heat treatment the gear wheel is subjected to surface hardening at a high temperature which causes deformations.After the heat treatment the gear wheel must be subjected to various other operations such as: grinding of the hole (if it is a gearwheel having a hole), grinding of the supports (if it is a shafted gear wheel), grinding of the faces (cleaning of the surfaces both of the teeth and of the non ground faces, and testing of the geometry of the gearwheel after the preceding operations). All these operations can cause further deformations and therefore reduce the quality of the gearwheel.

Moreover, the manipulation of the gearwheel during such operations can cause dents on the teeth of the gear wheel itself. Finally, the grinding of the hole or of the supports causes an eccentricity of the teeth with respect to the hole or the supports.

Among these errors the denting of the teeth can be detected by a testing device and can be eliminated by grinding, finding the dents visually or by utilising electronic systems or gears covered with abrasive material. In both cases it is possible to eliminate only small dents, such systems not being very effective.

Moreover, these operations are expensive both in terms of labour used and the time required. Finally, due to the low effectiveness of the said systems, gearwheel production plants have a significant quantity of scrap gear wheels which serve only to increase the cost of production.

The object of the present invention is that of providing a device for eliminating deformations and dents in the teeth of a gear wheel, which will be free from the said disadvantages, that is to say which will be of high efficiency thereby containing the final cost of these operations.

According to the present invention there is provided a device for eliminating deformations and/or dents in the teeth of a gear wheel, particularly in a phase subsequent to one in which a heat treatment is performed on the said gearwheel, characterised by the fact that it comprises a tool operable to mesh with the said gear wheel, means for pressing the said tool and said gearwheel together with a constant pressure, and a control member operable to transmit a rotary movement to the gear wheel or to the said tool; the said gear wheel and the said tool having respective axes which are inclined with respect to one another.

For a better understanding of the present invention a preferred embodiment is now described, purely by way of non limitative example, with reference to the attached drawings, in which: Figure 1 is a perspective view of a device operable to eliminate deformations and/or dents in the teeth of a gearwheel; Figure 2 is a partial view of a tool of the device of Figure 1; and Figure 3 is a perspective view of a tooth of the tool of Figure 2.

As illustrated in Figure 1, there is generally indicated with the reference numeral 1 a device operable to eliminate deformations and/or dents in the teeth of a gearwheel 2, particularly in a phase subsequent to one in which a heat treatment has been performed. The device 1 comprises a rotatable shaft3 on which are keyed a pulley4 and the gear wheel 2. The pulley 4 cooperates by means of a chain 5 with a pulley 6 keyed onto an output shaft 7 of an electric motor 8. The device 1 further includes a pneumatic piston 11 acting on a cylinder 12 supporting a tool 13 meshing with the gear wheel 2. A cylinder 12 is slidable along a hole formed in a support wall 14 and can be positioned at a predetermined angle with respect to its axis by the interposition of a bus 15 mounted within the said hole.The cylinder 12 is left with a small amount of piay to permitthetool 13to perform small oscillations about its axis. A substantially U-shape element 16 is fixed to the underside of the cylinder 12 and has two arms 17 between which is fixed a spindle 18 on which is freely mounted the tool 13. In particularthe axes of the tool 13 and of the gear wheel 12 are skew and lie in two planes which are parallel to one another.

With reference to Figures 2 and 3, the tool 13 has a plurality of teeth 21 covered with a material of great hardness such as, for example, titanium nitride. Each tooth 21 has on each face a plurality of grooves 22 in such a way as to define corresponding cutting edges. In place of the tool 13 there may be used a similar tool made of a very hard alloy and therefore without the covering material such as titanium nitride.

The operation of the device 1 is as follows.

In particular, the tool 13 is first of all made to mesh with the gear wheel 2 in such a way that there is no play on the faces of the teeth and then pressed against the gear wheel 2 itself by the action of the piston 11. Then the gear wheel 2 is put into rotation by operation of the motor 8 and the tool 13 can then, by the action of the cutting edges of its own teeth 21, work the gear wheel 2 and therefore eliminate possible deformations and/or dents. It is to be noted that the pressure with which the tool 13 is pressed against the gear wheel 2 remains constant during the working of the gearwheel 2. The possibility of having a constant pressure during the working allows the elimination of dents which are found in a region of the teeth in which the teeth of the gear wheel 2 are closest to the centre of rotation (negative eccentricity).In fact, if the tool 13 were at a fixed distance it would be possible for play to be created between the faces of the teeth which would prevent the removal of the material of the dent because the tool 13 would then contact the dent with a reduced pressure insufficient to effect cutting action. In the event, therefore, of the dents being located on a region of the gear teeth where the teeth are furthest from the centre of rotation (positive eccentricity) by utilising a tool 13 at a fixed distance an excessive load could be created between the faces of the teeth which could lead to breakage or damage of the tool itself. It is to be noted moreover that the pressure whilst remaining constant during working can be adjusted in dependence on the required degree of effectiveness in working and on the type of gear wheel to be finished.

By maintaining the pressure constant the tool 13, in the case of gear wheels 2 with a certain eccentricity, can vary in distance from the centre of rotation of the gearwheel 2 therefore being able to continue in rotation without any play on the faces of the teeth occurring. It is necessary for the axes of the gear wheel 2 and of the tooth 13 to be slightly skew so that during the rotation there will be a relative sliding velocity between them along the axis of the teeth; this permits the tool 13 to cut the rough edges or raised portions of material characteristic of dents.

Finally, it is to be noted that the cylinder 12 can assume predetermined angular positions with respecs to its axis in such away as to be able to have corresponding roations of the axis of the tool 13 (always in the same plane) and therefore to be able to work gear wheels with different teeth. As already described, the cylinder 12 is allowed to perform small oscillations about its own axis during the working, in such a way as to be able to work even gear wheels in which there are variations in the direction of the helix from one tooth to another.

From the preceding description the advantages achieved by the embodiment of the device are apparent.

In particular, the device 1 is of high efficiency in eliminating deformations and/or dents in the gear wheel 2. Moreover, being of simple construction it involves lower costs in production and its use in the cycle of operations for producing gear wheels causes a reduced working cost for these latter ensuring, at the same time (as already indicated) a high effectiveness such as to be able to remove dents of the order of even greater than 0.1 mm and at the same time to effect cleaning of the teeth .

Finally, it is clearthatthe device 1 described above can be modified and varied without departing from the protective scope of the invention.

In particular, different actuator means can be used in place of the piston 11. For example hydraulic or elastic-mechanical systems can be used. Moreover, the tool 13 can be made with a different form such that its action takes place above all in the regions where the dents are most frequently found. For example, the faces of each tool 21 could be concave for the purpose of eliminating dents which are located in the top and atthetwo ends of the tooth of the gear wheel 2. Also, it is possible to make the tool 13 rotate and mount the gear wheel 2 freely on the shaft 3. Finally, the gear wheels 2 to be worked can be different, for example shafted gear wheels, and likewise the systems for rotation of the cylinder 12 supporting the tool 13 about its own axis can be different.

Claims (11)

1. A device for eliminating deformations and/or dents in the teeth of a gear wheel, particularly after the gearwheel has been subjected to a heat treatment, characterised by the fact that it comprises a tool operable to mesh with the said gear wheel, means for pressing the said tool and the said gear wheel together with a constant pressure, and a control member operable to transmit rotary movement to the said gear wheel or to the said tool; the said gear wheel and the said tool having respective axes which are skew with respect to one another.

2. A device according to Claim 1, characterised by the fact that the said means include a pneumatic or hydraulic piston.

3. A device according to Claim 1, characterised by the fact that the said means include a thrust member of the resilient-mechanical type.

4. A device according to at least one of the preceding Claims, characterised by the fact that the said means support a spindle on which the said tool is freely rotatably mounted.

5. A device according to at least one of the preceding Claims, characterised by the fact that the said control member includes an electric motor operable to drive the rotary movement of a rotatable shaft on which the said gearwheel is keyed.

6. A device according to Claim 4 and/or Claim 5, characterised by the fact that the said means are rotatable about their axes in such a way that the said tool can assume a predetermined angular position with respect to the axis of the said means, thereby permitting the said tool to perform small oscillations about its own axis during the working cycle.

7. A device according to at least one of the preceding Claims, characterised by the fact that the said tool has a plurality of teeth on the faces of which there are formed a plurality of grooves in such a way as to define a plurality of cutting edges.

8. A device according to Claim 7, characterised by the fact that the faces of the said teeth are substantially concave.

9. A device according to Claim 7 and/or Claim 8, characterised by the fact that the said teeth are covered with a material of great hardness.

10. A device according to at least one of the preceding Claims, characterised by the fact that the said hard material covering the teeth of the said tool is a composition based on titanium nitride.

11. A device operable to eliminate deformations and/or dents in the teeth of a gear wheel as described and illustrated with reference to the attached drawings.