Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
5. 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
10. 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
15. carried out, un-til all tooth flanks have been machined.
Whilst grinding flnds widesplead 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 a suitable grinding procedure. It is true
20. 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 spiral-toothed bevel gears are particularly desirable,
since they have a large jump overlap and can be manufactured
25. by suitable design in such a manner that under load the
bearing surface wanders only s1ightly, whilst with single
sided positioned straight- and oblique-toothed bevel gears the
bearing surface under load wanders from the inner to the
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outer end of the tooth. As a result of their low sensitivity
to displacement and the favourable jump overlap, spiral-
toothed bevel gears have especially favourable noise properties.
`~ In procedures of the type described, which have become
5. known in practice, both wheels of each gear-wheel pair (wheel
and counter wheel) are machined with cup wheels which have
two conical grinding flanks and which are located in one tooth
gap during grinding. The grinding flanks are thus turned
away from each other and form a conical outer ringj which
10. projects concentrically to the axis of rotation of the grinding
disc from a plane which is orthogonal to the axis of rotation.
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
15. are necessary. Both flanks of each tooth gap of a wheel can
be ground in one operation by means o~ 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 corres-
- 20. pondingly high expenditure for measuring and control equipment.
~ If, on the other hand, both toothed wheels of a pair are
- ground in one operation, then on at least one tooth flank
the ~earing region (known as contact surface) does not lie
in the centre of the tooth flank, but at the edge of the
25. 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 prevlously ground gear wheel) in one operatlon and without
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expensive control procedures, so as to be an exact fit with
the 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
5. wheel) by the simultaneous grinding of the flanks on the two
sides of one tooth by means of a cup wheel having two grinding
flanks which are inclined towards each other and form a conical
inner ring. Thus, as hereinproposed the wheel and the counter
wheel are machined by different cup wheels. Whilst one of
10. the cup wheels has, as explained, grinding flanks which are
inclined away from each other, (that is to say mutually
outwardly facing), and form a conical outer ring, the counter
wheel is machined by a cup wheel of which the grinding flanks
are inclined towards each other, (that is to say mutually
15. inwardly facing)~ and in effect form a hollowed-out conical
inner ring concentric with the axis of rotation of the grinding
disc, in a plane orthogonal to the axis of rotation. The invention
is based on the appreciation that when grinding the gear
teeth by reference to the tooth gap as in the prior art,
20. 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
25. 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 counter wheel is ground by a
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cup wheel of which the contour is complementary to that
of the cup wheel which is grinding the wheel itself. The
axes of the two cup wheels naturally coincide in their
position with respect to the teeth to be ground.
Accoxding to a preferred feature, the cup wheel is
sub~ected to an additional motion, cyclic in nature and of
small eccentricity, 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,
lO. 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 flan~s.
In consequence of this a wide convexity is produced, which
15. 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 under simultaneous
20. cyclic motlon, the outer flank is ground during the outwards
part of this additional cyclic motion, and the inner flank of
a tooth gap is ground during the inwards part, so that the
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corresponding flanks of the counter wheel can be machined
in the same manner in one grinding procedure. By corresponding
25. 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
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particularl 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) bv form-grinding, but machining the pinion in accordance
5. with the above-named procedure.
-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 aup wheel remain in the direction of the circumference
10. 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
15. 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 rippin~ is reduced,
20. i.e~ work can be carried out at a higher rate of feed.
Diferent methods are available for production of the
additional motion. The additional motion can be a circular
motion about the a~is of the grinding disc, as already described.
In many cases it is advantageous for the additional motion
25. of the grinding disc to be over a varying path, made up from
two paths in the same direction with different radii of
curvature. By this means, shorter down times are obtainable,
during which the grinding disc is in contact with neither
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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
5. 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, wherehy the position of the bearing surface
10. 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 suhstantial improvement of
15. the meshing of the toothed wheels, but also to a favourable
in~luence on grinding burns by means of the corresponding
variation in closeness of fit between tooth flanks and
grinding flanks especially also o~ the sunken bevel inner
ring. In addition, the convexity, and with it the bearing
20. area, can be changed in an advantageous malmer in that the
grinding disc is disposed so as to be movable in the
direction of its axis, so that it grlnds on a diameter which
can be selectedO
The ratio between cutting speed and feed speed of the
25. 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
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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
5. 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
10. procedure described, the invention is based on a current
equipment for gear generation in the form of bevel gear
~ wheels, which includes a cup wheel which can be driven about
; a grinding axis and which has two conical grinding flanks.
In accordance with the invention such a device is characterised
15. in that the grinding flanks are inclined towards each other
and form a conical inner ring. ~ ~
The invention will now be described further, by way
of example only, with reference to the accompanying drawings
in which:-
20. Fig. 1 is a schematic illustration of the interlocking
relatlonships of a pair of wheels, and the
interlocking relationships between the grinding
disc and the wheel;
Fig. 2 shows a bevel wheel in the idealised form of a
25. crown wheel;
Fig. 3 is a perspective view of the bevel wheel to be
ground with the grinding disc shown in`partial
section;
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Fig. 4 shows a bevel wheel in the idealised form of
a crown wheel, showing the geometry and kinematics
: of the grinding wheel; and
Fig. 5 illustrates a number of examples for the path
5. followed by the cyclic motion.
Referring now to the drawings, Fig. 1 shows a pair
of gear wheels with two lntermeshing bevel gears 1 and 2
having spiral teeth. Each wheel 1, 2 has the same constant
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length R for the bevel, whilst the angles of bevel of the
~; 10. two wheels are denoted byJ Ol and ~02~ 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 clrcles Ra are shown projected
15. 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~drawlng). One tooth 10 of wheel l and
one tooth gap 20 of gear~wheel 2 are shown. If the two wheels
mesh with each other, an ideallsed plan may~be imagined, i~
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20. which the teeth have straight flank lines, which mesh
~; simultaneously wlth both wheels and whose points o~ contact
in all posltions of generation with the two wheels l, 2
:
are also simultaneously the points of contact of~the two
wheeIs one with another. This form of tooth arrangement -
25. known as the ideal crown wheel - is developed as tooth pro-
jection 3 between the two wheels l, 2. This ldeal tooth
arrangement of the bevel gear has an outer radius equal to
the outer bevel length ~ and an angle of bevel of 90 - and
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therefore a doubled angle of bevel of 180 . Fig. 2 is
a view from above of the ideal crown wheel 4 appertaining
to the two wheels, in which the flank lines which limit a
tooth gap gl, in this case 42, 43, are represented by arcs
5. 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 ~ig. l. With this
grinding disc, whose grinding flanks 51, 52 form a conical
outer, or "externa1'l ring, the right and the left flanks
lO. 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 l, 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
15. 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. l, whose conical
grinding flanks 71, 72 are inclined towards each other and
20. form a hollow sunken conlcal inner, or i'internall', rlng. By
this means i~ 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 crown
wheel used. While the grinding disc 5 grinds the tooth
25. gap 20 of wheel 2 by means of the grinding flanks 51, 52,
the flanks of tooth lO 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
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can be displaced in the direc-tion of a~is 8 in accordance
with arrow 81, so that the disc grinds on another diameter
~ence the convexity may be varied.
Fig. 3 shows a practical aspect of the method as applied
- 5. to the grinding of wheel 2. The grinding disc 5 with the
flank profile 51, 52 rests in the form of a conical outer
` ring on the spindle 53, which rotates in direction 54. This
'- rotary motion is the cutting motion of the grindlng disc.
The gear wheel 2 to be ground rests on an axle 23 arranged
10. ~or this purpose, i.e. a driving shaft, and executes an
oscillatory rotary motion- the gear-generating motion -
,
in the direction of the double arrow 24. The ~rinding disc5 executes, in addition to the cutting motion 54, a reciprocating
motion 56 adapted to the ~otion 24 of the bevel gear,
15. 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. ~s shown in Fig. 3, tooth gap 20 of the bevel gear
is being ground, and the flank 21 (below this in the drawing)
20. is being machined by the outex grinding flank 51, and the
upper flank 22 by the inner grinding flank 52. Thls leads to
machining o~ 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
25. the directions of the double arrow 24.
On the rotary or 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
f~
which is transmitted either from the grinding disc 5 through
grinding spindle 53, or directly from this latter. This
is further explained b~ means of the ideal crown wheel 6
shown in Fiaure 4, in which the cutting lines of a toot~
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 r and inner radius ri, which turns about
axis Ç3. 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. Both motions
take place in the direction of the arrow 65.
The radius OL curvature of the concave tooth flank is
- the sum of the radius r of the grlnding 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
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 w~eel are produced with
a grinding disc, a~ described in Figs. 1 and 3, 5 to 7 as
appropriate, and if either both or one only of the working
tools are subjected to such an additional motion, an advantageous
convexity is produced, leadin~ to a restricted lateral force
and thus favourable displacement properties of the wheel.
In addition, the wheel and the counter-wheel can be pxoduced
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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
5. in a single point, but actually o~er a relatively small
contact surface, on account of the cutting adjustment during
grinding. The size of this contact surface depends with regarcl
to the engaging surfaces on the mag~itude of the adjustment
and on the ratio of the cur~atures of the grinding disc and
10. the additional motion.
A further advantage of this procedure is seen in Fig. ~.
In the arrangement of the additional motion indicated, the
~ contact zone wanders on the concave flank from the outer end
- of the tooth to the inner end of the tooth. and on the convex
; 15. flank 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 durlng grinding, and hence the risk of grinding burns,
20. is reduced.
Various different~forms of producing the additional motion
are diagrammatically shown in FigO 5. 5.1 shows the
circular path which has already been explained. 5.2 shows
another cyclic curve, in which two sections of circular
250 arcs, of different radii, are combined. Whilst during a
circular additional motion in accordance with 5.1 there is a
large proximity time, this time is reduced by use of a form
of additional motion in accordance with 5.2. In addition
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there is a larger variation in width on selection of the
desired convexity.
With the path of the motion 5.3 there is a displacement
at the end positions, which has a component of motion in the
5. 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 5.4. By this means a
10. 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 grlnding precision gears, e.g. in machlne
15. 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 pxoductlon,
e.g. for lorries, the preliminary formation of the teeth
20. 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.
25.
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