GB1593225A

GB1593225A - Method of and means for grinding pairs of gear wheels as spiral or curved toothed bevel gear wheels

Info

Publication number: GB1593225A
Application number: GB18176/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-05-11
Filing date: 1978-05-08
Publication date: 1981-07-15
Also published as: FR2390233B1; BR7802973A; DE2721164C3; SE7805312L; BE866882A; IT7823284A0; LU79639A1; CA1103460A; CH628271A5; FR2390233A1; NL7804959A; IT1094826B; AT354885B; ATA319078A; SU1075954A3; SE434807B; DE2721164B2; DE2721164A1; JPS549090A

Abstract

When grinding spiral bevel gears (1, 2) by the indexing method, in each case two tooth flanks at one of the bevel gears (2) can be machined on both sides of a tooth gap in one operation with a cup grinding wheel (5), the grinding flanks (51, 52) of which form an outer bevel ring. To achieve the object of grinding a satisfactorily meshing mating gear (1) in one operation, it is proposed to use a cup grinding wheel (7) to grind the mating gear (1), the grinding flanks (71, 72) of which cup grinding wheel (7) face one another and form an inner bevel ring. To generate width crowning, a cyclic additional movement of slight eccentricity can be imparted to the grinding wheels (5, 7). <IMAGE>

Description

(54) METHOD OF AND MEANS FOR GRINDING PAIRS OF GEAR WHEELS AS SPIRAL OR CURVED TOOTHED BEVEL GEAR WHEELS (71) I, DIETER WIENER, a citizen of the Federal Republic of Germany, of 9 Tulpenstrasse, D-7505 Ettlingen-Bruchhausen, Federal Republic of Germany, do hereby declare the invention, for which I pray that a Patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention is concerned with a method of and a means for grinding pairs of spiral or curved tooth bevel gears in the gear generating process, in which the teeth of one of the gears are produced by grinding the flanks at the two sides of a tooth gap by a cup wheel having two mutually outwardly facing grinding flanks and which form a bevelled outer ring.

During the grinding of gear wheels by the gear generation procedure, the gear wheel to be ground, on the one hand, and the grinding disc, on the other hand, describe synchronized movements with respect to each other, the movements being coupled together through the driving train of the gear grinding machine. After each gear generating procedure, in which one or two tooth flanks are ground, the gear wheel is indexed forward, and a further gear generating procedure is carried out, until all tooth flanks have been machined.

Whilst grinding finds widespread use for spur gears, grinding of bevel gears has hitherto been used only to a small extent.

This is mainly due to the high cost of grinding and to the lack of suitable grinding procedure. It is true that bevel gears with straight and oblique teeth can be ground, but no grinding procedure is known by which spiral-toothed bevel gears can be satisfactorily ground. Many applications of spiraltoothed bevel gears are particularly desirable, since they have a large intermeshing tolerance and can be manufactured by suitable design in such a manner that under load the bearing surface location varies only slightly, whilst with single sided positioned straight- and oblique-toothed bevel gears the bearing surface location under load varies from the inner to the outer end of the tooth.

As a result of their low sensitivity to displacement and the favourable intermeshing tolerance, spiral-toothed bevel gears have especially favourable noise properties.

In procedures of the type described, which have become known in practice, both wheels of each gear-wheel pair (wheel and counter wheel) are machined with cup wheel grinding discs which have two conical grinding flanks and which are located in one tooth gap during grinding. The grinding flanks are on radially inner and outer surfaces of an axially extending annulus, which is concentric with the axis of rotation of the grinding disc and extends from the plane thereof which is orthogonal to the axis of rotation, the surfaces converging away from the plane of the disc. It is true that accurately meshing pairs of gears can be produced by this method, but only after considerable expenditure of time, because expensive and complicated control procedures are necessary. Both flanks of each tooth gap of a wheel can be ground in one operation by means of this known procedure.But for the counter wheel each flank must be matched to the corresponding flank of the wheel. This necessitates the carrying out of two operations under expensive control with a correspondingly high expenditure for measuring and control equipment. If, on the other hand, each toothed wheel of a pair is ground in one operation, then on at least one tooth flank the bearing region (known as contact surface) does not lie in the centre of the tooth flank, but at the edge of the tooth (known as edge contact).

The object of the invention is to provide a method of and means for grinding the tooth flanks of the counter wheel (to a previously ground gear wheel) in one operation and without expensive control procedures, so as to be.an exact fit with teeth of the wheel.

This object is attained in accordance with the invention, by the formation of the teeth of the other bevel gear (counter wheel) by the simultaneous grinding of the flanks on the two sides of one tooth by means of a second cup wheel grinding disc having two concentric annuli extending axially from the plane of the disc and whose two grinding flanks face each other and converge towards the plane of the disc. Thus, as hereinproposed the wheel and the counter wheel are machined by different cup wheels. Whilst one of the cup wheels has, as explained, grinding flanks which face away from each other, and form a conical axially extending annulus, the counter wheel is machined by a cup wheel of which the grinding flanks face each other, and in effect form a conical annular axially extending groove concentric with the axis of rotation of the grinding disc.The invention is based on the appreciation that when grinding the gear teeth by reference to the tooth gap as in the prior art, due to the geometry of the tooth arrangement, during grinding of the counter wheel in one operation only one of the two tooth flanks of each tooth gap (therefore only the left or only the right hand flank) can be so ground that the direction of its flank agrees with that of the corresponding flank of the wheel which has already been ground, and therefore meshes accurately with it. The solution of the problem in accordance with the invention consists essentially of carrying out the grinding procedure accurately symmetrically for wheel and counter wheel, in that the wheel and counter wheel are ground by cup wheels of which the contours are complementary. The axes of the two cup wheels naturally coincide in their position with respect to the teeth to be ground.

According to a preferred feature, the cup wheel is subjected to an additional motion, cyclic in nature and of the axis of rotation of the cup wheel parallel with itself, during grinding. Such an additional motion can be effected, for example, by moving the axis of rotation of the grinding disc parallel to itself in a circular orbit, by means of an eccentric bearing box, for example. An analysis of the conditions shows that the additional eccentric motion influences the curvature of the concave tooth flanks differently from the curvature of the convex tooth flanks. In consequence of this a wide convex curvature is produced, which leads in an advantageous manner to a limited lateral bearing surface with the consequence that within certain limits displacements of the axes of the gear wheels meshing with each other can be permitted.

During rotation of the grinding disc with a simultaneous cyclic motion, the concave flank is ground during the part of this additional cyclic motion in which the centre of the disc is nearest to the gap, and the convex flank of the tooth gap is ground during the part in which the centre of the disc is furthest therefrom, so that the corresponding flanks of the counter wheel can be machined in the same manner in one grinding procedure. By corresponding choice of the diameter of the grinding disc on the one hand, and of the diameter of the cyclic curve followed by the grinding disc on the other hand, the wheel and the counter wheel can be ground so as to give optimum fit together.In particular, there is also the advantageous possibility of machining one of the wheels of a pair, in general the one with the larger number of teeth (i.e. the so-called rim gear) by formgrinding with the known form of grinding disc, but machining the pinion in accordance with the above-described second form of grinding disc.

An advantage arising from the additional motion is that the danger of grinding burns is greatly reduced. During grinding without additional motion the grinding flanks of the cup wheel remain in the direction of the circumference along a line, known as the generator, so that one grinding stroke can move over the whole width of the tooth in one engagement, with the workpiece held in position. This leads to a considerable danger of burning and ripping during the grinding, so that grinding can be carried out only at a low rate of feed. If, on the other hand, grinding is carried out with the cyclic additional motion as explained, then the contact between gear wheel and grinding disc is reduced from a contact line to a closely localised contact region, so that the danger of grinding burns and grinding ripping is reduced, i.e.

work can be carried out at a higher rate of feed.

Different methods are available for production of the additional motion. The additional motion can be a circular motion about the axis of the grinding disc, as already described. In many cases it is advantageous for the additional motion of the grinding disc to be over a varying path, made up from two paths traversed in sequence with different radii of curvature. By this means, shorter down times are obtainable, during which the grinding disc is in contact with neither flank.

This also permits a larger variation in the convexity available. In addition, it is possible, between the curved sections of the path, to provide a section in which the motion is approximately perpendicular to the flank of the tooth, whereby the play between the profile strength of the grinding disc and the width of the tooth gap of the bevel gear can be equalised by a simple means. Finally, the mid-points of the two curved sections of the path can be located at different points, whereby the position of the bearing surface on one tooth flank can be varied with regard to the other tooth flank.

In each case the additional cyclic motion, combined with the method of working as explained in accordance with the invention, leads not only to a substantial improvement of the meshing of the toothed wheels, but also to a favourable influence on grinding burns by means of the corresponding variation in closeness of fit between tooth flanks and grinding flanks especially in the case of the converging annular groove. In addition, the convex curvature, and with it the bearing area, can be changed in an advantageous manner in that the grinding disc is disposed so as to be movable in the direction of its axis, so that it grinds on a diameter which can be selected.

The ratio between cutting speed and feed speed of the grinding disc lies preferably between 30:1 and 60:1, where the feed is defined as the motion of the contact point of grinding disc and wheel in the direction along the tooth. Further; it has shown itself to be advantageous for the cutting motion and the additional motion of the grinding disc to be arranged in directions opposite to each other, thus grinding in contrary motion.

Grinding in contrary motion is known in itself, but has no advantage in current grinding procedures. On the other hand, within the framework of the invention, there is the advantage that higher feed quantities (rate of removal of material) are possible than with grinding with the same path.

With regard to the equipment for carrying out the procedure described, the invention provides novel equipment for gear generation in the form of bevel gear wheels, which includes a cup wheel grinding disc which can be driven about a grinding axis and which has two grinding flanks, and in accordance with the invention such a device is characterised in that the grinding flanks face each other and form a conical, axially extending, annular recess converging towards the plane of the grinding disc.

The invention will now be described further, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic illustration of the inter locking relationships of a pair of wheels, and the interlocking rela tionships between the grinding disc and the wheel; Fig. 2 shows a bevel wheel in the form of an imaginary crown wheel; Fig. 3 is a perspective view of the bevel wheel to be ground with the grinding disc shown in partial section; Fig. 4 shows a bevel wheel in the form of an imaginary crown wheel, showing the geometry and kinematics of the grinding wheel; and Fig. 5 illustrates a number of examples for the path followed by the cyclic motion.

Referring now to the drawings, Fig. 1 shows a pair of gear wheels with two intermeshing bevel gears 1 and 2 having spiral teeth. Each wheel 1, 2 has the same constant length R for the bevel, whilst the angles of bevel of the two wheels are denoted by 80, and 802, respectively. Finally, both wheels have an outer bevel length Ra. In addition, in the example illustrated the tooth height is independent of the bevel length R.

The outer peripheries of bevel gears 1 and 2 are shown projected onto the plane of the drawing to the right of the pair of gear wheels, and are consequently shown as ellipses, (in dotted lines on the drawing).

One tooth 10 of wheel 1 and one tooth gap 20 of gear wheel 2 are shown. If the two wheels mesh with each other, a hypothetical line of tooth-like form may be imagined, of which the teeth have straight flank lines, which teeth mesh simultaneously with both wheels and whose points of contact in all positions with the two wheels 1, 2 are also simultaneously the points of contact of the two wheels one with another. This form of tooth arrangement - shown as an imaginary crown wheel - is developed as tooth projection 3 between the two wheels 1, 2.This tooth arrangement of the bevel gear is in the form of a crown wheel having an outer radius equal to the outer bevel length Ra and an angle of bevel of 90" - and therefore a doubled angle of bevel of 1800. Fig. 2 is a view from above of the imaginary crown wheel 4 appertaining to the two wheels, in which the flank lines which limit a tooth gap 41, in this case 42, 43, are represented by arcs of circles.

In the known method of grinding bevel wheels the working tool takes the form of a cup-shaped grinding disc 5, as shown at the right hand side of Fig. 1. With this grinding disc, whose grinding flanks 51, 52 form a conical axially extending annulus, the right and the left flanks of the tooth gap 20 of one gear wheel 2 are produced. If this tool is also used in the production of the tooth gap of the other gear wheel 1, the right hand and left hand flanks of such gap must be produced in separate processes, otherwise the mid-points of the flank lines of the right hand and left hand flanks of the tooth gap of the wheel and counter wheel would not coincide.

Accordingly, in accordance with the invention, the counter-wheel is machined by a cup wheel 7, Fig. 1, whose grinding flanks 71, 72 face each other and form an axially extending conical annular groove. By this means it is possible to machine the counter-wheel also in one operation. In addition it is shown how the grinding discs 5 and 7 have the same axis 8 with respect to the imaginary crown wheel 3. While the grinding disc 5 grinds the tooth gap 20 of wheel 2 by means of the grinding flanks 51, 52, the flanks of tooth 10 of counter-wheel 1 which mesh with such tooth gap 20 are ground by means of the grinding disc 7, each in one operation. The grinding disc 7 with its spindle can be displaced in the direction of axis 8 in accordance with arrow 81, so that the disc grinds on a larger or smaller diameter. Hence the convex curvature may be varied.

Fig. 3 shows a practical aspect of the method as applied to the grinding of wheel 2.

The grinding disc 5 with the grinding flanks 51, 52 in the form of a conical annulus is attached to the spindle 53. which rotates in a direction shown by arrow 54. This rotary motion is the cutting motion of the grinding disc. The gear wheel 2 to be ground is attached to an axle 23 arranged for this purpose, i.e. a driving shaft, and executes an oscillatory rotary motion - the geargenerating motion - in the direction of the double arrow 24. The grinding disc 5 executes, in addition to the cutting motion 54, a reciprocating motion 56 adapted to the motion 24 of the bevel gear, for the production of which a component is used which moves the grinding disc in a cyclic motion about the intersection 57 of axle 23 of the wheel 2 with the centre line 58 of the tooth height.As shown in Fig. 3, tooth gap 20 of the bevel gear is being ground, and the flank 21 (below this in the drawing) is being machined by the outer grinding flank 51, and the upper flank 22 by the inner grinding flank 52. This leads to machining of one of the flanks 21 or 22 from the outside inwards, and that of the other flank from the inside outwards, always while the wheel is reciprocating in one or other of the directions of the double arrow 24.

On the rotary cutting motion 54 of the grinding disc 5, corresponding to the grinding disc 7, there is superimposed an additional cyclic motion 55 of small eccentricity which is transmitted either from the grinding discS through grinding spindle 53, or directly from this latter. This is further explained in relation to the imaginary crown wheel 6 shown in Figure 4, in which the cutting lines of a tooth gap are indicated by 61 and 62.

The flanks of the tooth gap are produced by a grinding disc, not shown in the drawing, of outer radius ra and inner radius ri, which turns about axis 63. Again this rotary motion is the cutting motion. In addition the grinding disc executes a cyclic motion, which is circular in the aspect of the invention illustrated here, whose orbit is indicated by 64 in the drawing.

The two motions take place in the direction of the arrows 65.

The radius of curvature of the concave tooth flank 61 is the sum of the radius ra of the grinding disc and the radius of the additional motion. The cutting line of this concave form is likewise an arc of a circle. The convex tooth flank 62 has in this plane only approximately the form of an arc of a circle, since the two motions overlap along the radius ri and the radius of the additional motion. The curvature of this tooth flank corresponds approximately to the reciprocal of the radius ri and is larger than this reciprocal by a negligible amount.If the wheel and the counter wheel are produced with a grinding disc, as described in Figs. 1 and 3, and also 5 as appropriate, and if either both or one only of the working tools are subjected to such an additional motion, an advantageous convex curvature is produced, leading to a restricted lateral force between meshing teeth and thus favourable displacement properties of the wheel. In addition, the wheel and the counter-wheel can be produced each in one process. Contact between grinding disc and workpiece takes place not only along a contact line, which lies essentially in the cutting direction of the grinding disc, but, on superimposition of a reciprocating motion, theoretically in a single point, but actually over a relatively small contact surface, on account of the cutting adjustment during grinding.The size of this contact surface depends with regard to the engaging surfaces on the magnitude of the adjustment and on the ratio of the curvatures of the grinding disc and the additional motion. The cutting motion is preferably counter to the additional motion and the ratio of cutting speed to feed speed is preferably 30:1 to 60:1.

A further advantage of this procedure is seen in Fig. 4. In the arrangement of the additional motion indicated, the contact zone varies on the concave flank 61 from the outer end of the tooth to the inner end of the tooth, and on the convex flank 62 from the inner end of the tooth to the outer end of the tooth. Due to the form of the additional motion and the limited length of the contact surface between grinding disc and wheel being produced, the effect of heating on the wheel during grinding, and hence the risk of grinding burns, is reduced.

Various different forms of producing the additional motion are diagrammatically shown in Fig. 5. 5.a shows the circular path which has already been explained. 5.b shows another cyclic curve in which two sections of circular arcs, of different radii, are combined.

Whilst during a circular additional motion in accordance with 5.a there is a large inoperative time, this time is reduced by use of a form of additional motion in accordance with 5.b.

In addition there is a larger variation in width on selection of the desired convexity.

With the path of the motion 5.c there is a displacement at the end positions, which has a component of motion in the direction of the circumference of the wheel. By this means a balancing of the play between the thickness of the grinding disc and the width of the tooth gap can be effected.

Finally, the mid-points of the additional motion can be selected as desired as is shown in 5.d. By this means a favourable influence of the position of the bearing surface on one tooth flank is possible, independent of the position of the bearing surface on the other tooth flank.

The method of working as explained is especially advantageous for grinding precision gears, e.g. in machine tool production, press construction, fast-moving drives, and in aircraft production. The preliminary formation of the teeth is, in general, carried out by milling, after which the wheels are hardened and then ground. In mass production, e.g. for lorries, the preliminary formation of the teeth may be by precision forging, after which the wheels are hardened and then ground. Further, it is possible for one wheel usually that with the greater number of teeth - to be produced by grinding to shape, and for the counter-wheel to be machined in accordance with the procedure explained.

WHAT I CLAIM IS: 1. A process for the grinding of pairs of spiral or curved tooth bevel gears using a method of gear generation in which the teeth of one of the bevel gears are produced by grinding the flanks of a tooth gap by means of a first cup wheel grinding disc having two grinding flanks which are the radially inner and outer surfaces of an annulus extending axially from the disc, wherein the teeth of the other bevel wheel are produced by the simultaneous grinding of the flanks on the two sides of a tooth by means of a second cupwheel grinding disc having two concentric annuli extending axially from the plane of the disc and whose facing grinding flanks form a conical annular groove converging towards the plane of the disc.

2. A process as claimed in claim 1, wherein an additional cyclic motion of the axis of rotation of the cup wheel parallel with itself is superimposed on at least one of said cup-wheels during grinding.

3. A process as claimed in claim 2, characterised in that the cyclic motion is a circular motion.

4. A process as claimed in claim 2, wherein the cyclic motion is comprised of two sections whose paths are of different curvature and which are concave with respect to the curvature of the flanks of the teeth.

5. A process as claimed in claim 4, wherein the cyclic motion comprises, between the two sections of the motion whose paths are arcs of circles, a straight section of the motion substantially perpendicular to the.

flank of the tooth.

6. A process as claimed in claim 4 or 5, wherein the two circular shaped sections of the motion have different centres of curvature.

7. Apparatus for use in grinding pairs of spiral or curved tooth bevel gears comprising a cup-wheel grinding disc mounted for rotation about a grinding axis and having two concentric, axially extending annuli forming a conical annular groove converging towards the plane of the disc and whose facing surfaces form grinding flanks.

8. Apparatus as claimed in claim 7, wherein the cup-wheel grinding disc is adapted to be displaced in the direction of its axis.

9. Apparatus as claimed in claim 7 or 8, characterised in that the ratio of cutting speed to feed speed of the cup-wheel lies between 30:1 and 60:1, where the feed is the motion of the point of contact along the tooth.

10. Apparatus as claimed in any one of claims 7 to 9, characterised in that the cutting motion and the feed motion of the grinding disc are in opposite directions.

11. A process for grinding pairs of spiral or curved tooth bevel gears substantially as hereinbefore described with reference to and as illustrated in the various figures of the accompanying drawings.

12. Apparatus for grinding pairs of spiral or curved tooth bevel gears substantially as hereinbefore described with reference to and as illustrated in the various figures of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. circumference of the wheel. By this means a balancing of the play between the thickness of the grinding disc and the width of the tooth gap can be effected. Finally, the mid-points of the additional motion can be selected as desired as is shown in 5.d. By this means a favourable influence of the position of the bearing surface on one tooth flank is possible, independent of the position of the bearing surface on the other tooth flank. The method of working as explained is especially advantageous for grinding precision gears, e.g. in machine tool production, press construction, fast-moving drives, and in aircraft production. The preliminary formation of the teeth is, in general, carried out by milling, after which the wheels are hardened and then ground. In mass production, e.g. for lorries, the preliminary formation of the teeth may be by precision forging, after which the wheels are hardened and then ground. Further, it is possible for one wheel usually that with the greater number of teeth - to be produced by grinding to shape, and for the counter-wheel to be machined in accordance with the procedure explained. WHAT I CLAIM IS:

1. A process for the grinding of pairs of spiral or curved tooth bevel gears using a method of gear generation in which the teeth of one of the bevel gears are produced by grinding the flanks of a tooth gap by means of a first cup wheel grinding disc having two grinding flanks which are the radially inner and outer surfaces of an annulus extending axially from the disc, wherein the teeth of the other bevel wheel are produced by the simultaneous grinding of the flanks on the two sides of a tooth by means of a second cupwheel grinding disc having two concentric annuli extending axially from the plane of the disc and whose facing grinding flanks form a conical annular groove converging towards the plane of the disc.

flank of the tooth.