Improvements in Speed-varying Gear.
Year: 1890

page_text: PROVISIONAL SPECIFICATION.
Improvements in Speed-varying Gear.
I, WILLLIAM JOHN MUNDEN, of 70, Balcombe Street, Dorset Square, in the
County of London, Engineer, do hereby declare the nature of this invention to be
as follows:-
This invention relates to apparatus for enabling the speed of a driven shaft to be
varied from that of the driving shaft at will; and consists in its simplest form of a
worm-wheel, of a pitch varying from one end of the tooth to the other, upon the
driving shaft, and a similar wheel, gearing with the first, upon the driven shaft,
which latter is placed at an angle (preferably of 90°) with the driving shaft, and
with their axes in different planes. The width of the rims of these wheels, and
consequently the length of the teeth from end to end is greater than the width of
the band of actual contact between the teeth, and consequently by sliding each
wneel longitudinally upon or with its shaft, a different part of the teeth can be
caused to engage. The pitch or angle of the teeth (as hereinbefore stated) varies
from one end to the other, and it is evident that the slightest movement of the
wheels longitudinally will cause a different ratio of speed of the driven to the
driving wheel, and of course of the shafts, as the wheels and shafts are so connected
as to revolve together, although the wheels may in some cases slide longitudinally
upon the shaft, a feather and groove being used in this case. In a more complete
form the apparatus consists of two of the hereinbefore described worm-wheels with
their shafts parallel and the rims of the wheels at such distance apart as to admit of
a third similar wheel being placed between them with its axis at an angle of
about 90° with the plane of the axes of the other wheels, and gearing with both
of these. Each of the three wheels is enabled to slide longitudinally upon or with
its shaft, and by sliding these in such manner as to cause different parts of the width
of the rims to engage with each other, the ratio of speed between the first and third
shafts can be varied twice as much as when only two wheels and shafts are used.
And by increasing the number of wheels to four, the power of variation may be four
times and so on with any number ofwheels.
In general it is found necessary to provide means of simultaneously sliding each
shaft, or each wheel upon its shaft, longitudinally to the extent necessary to secure
the required ratio of speed between the driving and driven shafts, and this may in
some cases be determined by a screw, or by a micrometer and screw, or by any
other suitable means of ensuring a sufficiently exact adjustinent for the particular
operation in hand.
The foregoing description assumes the use of worm-wheels with their teeth upon
the outside cylindrical surface or face of each, but it is obvious that wheels the faces
of which are parts of the surfaces of cones may be used in some cases, or the faces
of the teeth engaged may he of any suitable curve, or the face of one wheel may be
curved and the other straight, in which latter cases one or both wheels may, instead
of sliding receive a motion through an are of a circle, as a means of effecting the
bereinbefore mentioned adjustment for varying speed.
Dated this 27th day of February 1890.

page_text: COMPLETE SPECIFICATION.
Improvements in Speed-varying Gear.
I, WILLIAM JOHN MUNDEN, residing at 106, Priory Park Road, Kilburn,
formerly of 70, Balcombe Street, Dorset Square, both in the County of London,
Engineer, do hereby declare the nature of this invention, and in what manner the
same is to be performed, to be particularly described and ascertained in and
by the following statement:-
This invention relates to apparatus for enabling the speed of a driven shaft to be
varied from that of the driving shaft at will, and consists in its simplest form of a
worm wheel (of a pitch varying from one end of the tooth to the other) upon the
driving shaft, and a similar wheel, gearing with the first, upon the driven shaft,
which is placed at an angle (preferably of 90°) with the driving shaft, and with
their axes in different planes. The width of the rim of each of these wheels, and
consequently the length of the teeth from end to end is greater than the width of
the band of actual contact between the teeth, and consequently by sliding each
wheel longitudinally upon or with its shaft, a different part of the teeth can be
caused to engage. The pitch or angle of the teeth, as herein before stated varies
from one end to the other, and it is evident that the slightest movement of the
wheels longitudinally will cause a different ratio of speed of the driven to the driving
wheel and of course of the shafts, as the wheels and shafts are so connected as to
revolve together although the wheels may in some cases slide longitudinally upon
the shaft, a feather and groove being used in this case.
In a more complete form the apparatus consists of two of the herein before
described worm wheels, with their shafts parallel, and the rims of the wheels at such
distance apart as to admit of a third similar wheel being placed between them with
its axis at an angle of about 90° with the plane of the axes of the other wheels, and
gearing with both of these. Each of the three wheels is enabled to slide longi-
tudinally upon or with its shaft, and by sliding these in such manner as to cause
different parts of the width of the rims to engage with each other, the ratio of
speed between the first and third shafts can be varied twice as much as when only
two wheels and shafts are used. And by increasing the number of wheels to four
the power of variation may be four times, and so on with any number of wheels.
In general it is found necessary to provide means of simultaneously sliding each
shaft, or each wheel upon its shaft, longitudinally to the extent necessary to secure
the required ratio of speed between the driving and driven shafts, and this may in
some cases be determined by a screw, or by a micrometer and screw, or by any
other suitable means for ensuring a sufficiently exact adjustment for the particular
operation in hand.
The foregoing description assumes the use of worm wheels with their teeth upon
the outside cylindrical surface, or face of each, but it is obvious that wheels the
faces of which are parts of the surfaces of cones may be used in some cases; or the
faces of the teeth engaged may be of any suitable curves, or the face of one wheel
may be curved and the other straight, in which latter cases one or both wheels may
instead of sliding receive a motion through an are of a circle, as a means of effecting
the herein before mentioned adjustment for varying speed.
In the accompanying drawings, in which like letters refer to like parts, or to
parts which serve the same purpose:—
Fig. 1 is a plan of the simplest form of apparatus.
Fig. 2 is an elevation of same.
Fig. 3 is a view of the teeth of a part of a worm wheel, shown as if developed or
unrolled from its circular form to a flat plane to assist in the explanation.
Fig. 4 is a plan of a modification in which the driving and driven shafts are
parallel and have a third intermediate shaft and wheel.
Fig. 5 is an elevation of same.

page_text: Fig. 6 is an end elevation of the fixed headstock and bed of a lathe with the
gearing applied thereto.
Fig. 7 is a modification in which one of the worm wheels is divided into three
widths, only one of which is engaged at the same time.
Fig. 8 is a modification in which each wheel is divided into three widths.
Fig. 9 is a modification in which each wheel is slightly tapered longitudinally, or
shaped like a truncated cone
Fig. 10 is a modification in which the surface of one wheel is slightly convex, and
the surface of the other slightly concave.
It will be understood that all the latter figures, (from 4 to 10 inclusive) are more
or less diagrammatic, and that each of the wheels have teeth upon their curved
surfaces of the description shown and described with reference to Figs. 1 to 3; and
also that means are provided where necessary, to cause each wheel to simultaneously
slide longitudinally upon or with its shaft to the extent necessary to ensure the
contact of the right parts in each case, such means being either similar to, or
substitutes or equivalents for that shewn in Figs. 1 and 2.
Referring now to Figs. 1 and 2, A designates the driving and B the driven
shafts. A is free to revolve in bearings a on brackets a' attached to base b*; and
has fixed upon it a feather ax. The worm wheel C with its extension c is bored to
fit this shaft, so as to slide easily upon it, but is prevented from turning on it by a
groove in the bore, which fits the feather ax upon the shaft. The shaft B is free
to revolve in bearings 6 in base 6x and frame 61. The worm wheel D is bored to
fit and slide freely upon this shaft B but is prevented from turning upon it by the
feather a similar to that on shaft A. Upon the base 6* are fixed brackets having
bearings in which rocks the shaft E which has rigidly attached to it two pairs of
arms F and G. The ends f of one pair F of these arms take into a groove turned
in the extension c of worm wheel C; and the ends g of the other pair of arms G take
into a similar groove in the extension d of worm wheel D. The shaft E has
ixed to it at one end the long arm g' at the extreme end of which is the projecting
part g2 which fits into, and moves up or down with, a slot formed in the lower end g
of the screw g³. This screw has a wing nut gt upon it which is free to revolve in a
slot in the upper part of a bracket go fixed to the base bx. The wing nut is
grooved where it fits over the upper part of the bracket 96, and so is unable to
move up or down, and it is obvious that by turning the nut 4, the screw will be
raised or lowered carrying with it the end g² of arm g'. This movement causes the
shaft E to rock and with it the arms F and G, carrying with them the worm
wheels C and D respectively in a longitudinal direction each relatively to its own
axis.
Referring now to Fig. 3 it will be seen that the angle or pitch of the worm wheel
teeth n, m, o varies from one side to the other. In Fig. 3 as well as in Figs. 1
and 2 it is shown in the middle of the worm wheel at point m as at an angle of 45°
with that plane of the axis which passes through the point m. This angle is shewn
by line X, X. The pitch increases to the right hand side until at the point
marked n, it is at an angle of about 30° (shewn by line Y, Y,) with same; and
decreases to the left hand side until at the point marked o, it is at an angle of
about 60°, (shewn by line Z, Z,) with the same plane. The practical effect of this
is the same as if the worm wheel was divided into three separate worm wheels, the
bands of contact being represented by the points m, n and o, with the additional
advantage that any point or band of contact may be chosen, and that these may be
varied or adjusted by longitudinally sliding each wheel simultaneously, while they
are in motion. It will be obvious, as shewn in Fig. 2, (assuming these wheels to be
constructed with angles as herein before referred to), that when the wing nut g is
rotated, and the screw ³ lowered until the long arin g is in a horizontal position,
the arms F will be in a vertical, and the arms G in a horizontal position,
and that while moving to these positions they will have pushed the worm wheels Ć
and D into their middle positions, thus bringing the teeth in each wheel into contact
at the points m. Now the teeth at these points, as hereinbefore stated, are at an

page_text: angle of 45°, or equal pitch with each other, and consequently one revolution of
shaft A and worm wheel C, will cause one revolution of shaft B and worm wheel D..
If the nut and screw g³ be manipulated to bring the wheels into the position
shewn in Figs. 1 and 2, the band of contact will be at points o in worm wheel C
and at points n in worm wheel D, which means that the driving teeth will be at an
angle of about 60° and the driven teeth at an angle of about 30°, and consequently
the driven shaft B and worm wheel D will make only about one revolution to two
of the driving shaft A. and worm wheel C. And when the wheels are moved to the
farthest extent in the opposite direction, (the arms then assuming the positions
shewn in chain-dotted lines) the band of contact will be at the points n and o
respectively in wheels C and D and consequently the driven shaft B and worm
wheel D would revolve twice to each revolution of driving shaft A and worm
wheel C. And this remains equally true for all positions of the arm g¹ and
worm wheels C and D, so that by means of the screw the finest adjustment is
possible of the relative speed of the driven shaft B to that of the driver A; and
where exceptionally delicate adjustment is necessary, the addition of a micrometer
to the nut and screw renders this easily attainable. It will thus be seen that with
the simplest form of apparatus, as shewn in Figs. 1 and 2, and assuming the number
of revolutions of the driving shaft A at 100 per minute, we have the power of
varying the number of revolutions of the driven shaft B from 50 to 200 per minute
by turning the wing nut g.
Figs. 4 and 5 shew a modification of the apparatus in which two vertical shafts,
A being the driver and B the driven, have each 8 worm wheel (C and D
respectively) sliding upon but revolving with them, by reason of the feathers a*.
An intermediate shaft A¹, likewise with feather ax has sliding upon but revolving
with it duplicate worm wheels C', C', these being formed integral with each other.
The teeth upon all these wheels being of varying pitch, as herein before described,
by simultaneously sliding them longitudinally upon their shafts different bands of
contact are brought into operation; and if we assume the same varying power for
each pair, as described with reference to Figs. 1 and 2, it will be seen that if the
speed of A is 100 per minute, the speed of B may be varied from 25 to 400 per
minute.
Fig. 6 shews a form of the apparatus, very nearly resembling the foregoing,
applied to a screw cutting lathe, A the driving shaft being the mandrel of the
lathe, and B, the driven shaft, the end of the leading screw used for screw-cutting.
In this case the intermediate worm wheels C¹ are some distance apart, but formed
integral with the intermediate shaft A' and sliding longitudinally bodily with it
to cause a different band of contact in wheels C¹ to engage with wheels C and D.
Fig. 7 shews a form of the apparatus in which one of the worm wheels, (here
shewn as the driver, but might equally well be the driven) is grooved circum-
ferentially so as to divide the length of the worm wheel into three bands which
have teeth of varying pitch upon them the same as the before described worm
wheels.
Fig. 8 shews a form of apparatus in which both wheels are divided the same as
the one in Fig. 7. It is necessary in each of these cases that the dividing grooves
be of less width than the bands of contact left remaining, so as to secure the teeth
of one baud engaging with the teeth of the other wheel before the teeth of the
preceding band has left it. Otherwise the number and width of grooves may be
left to choice.
Fig. 9 is a form of apparatus, similar to that shewn in Figs. 1 and 2 except that
each worm wheel is made slightly tapering so as to form a truncated cone, and the
large end of one engages with the small end of the other.
Fig. 10 is a modification in that it uses a pair of worm wheels one of which has
concave, and the other convex working surfaces. The degree of concavity and con-
vexity is much exaggerated in the drawing.
Throughout the drawings the arrows show the direction of longitudinal move-
ment for varying the speed ratio,

page_text: In the foregoing description the worm wheels are shewn either as sliding on or
with their shafts. I do not however restrict myself to these particular construc-
tions, but use any form which enables me to ensure each wheel sliding in the
direction of its axis, and revolving only with its own shaft. And with respect to
the mechanism for causing such movement I use any which enables me to secure
simultaneous or approximately simultaneous movement of each of the wheels in
the particular form of apparatus employed. Any number of wheels may be used;
and although in the forins shewn, the planes of the axes of each working pair are
shewn as at right angles to each other, yet they may be placed at any angle at
which a worm and wheel of the common type would work.
Among the many possible applications of this invention may be mentioned the
screw-cutting lathe, in which a simple form of the apparatus (as shewn diagram-
matically in Fig. 6) would enable any ordinary thread to be cut without the use
of change wheels; varying the cut in shop tools generally; starting gas engines, or
electrically propelled vehicles; regulating clocks and watches by varying (auto-
matically in some cases) the ratio of speed of any two spindles instead of varying
the length of the pendulum or hair spring, and innumerable others.
Having now particularly described and ascertained the nature of my inven-
tion, and in what manner the same is to be performed, I declare. that what I
claim is :-
1. The use of two or more worm wheels engaging with each other, and having
the teeth of each of increasing pitch or angle from end to end substantially as
described and shewn.
2. A speed varying gear consisting of two or more worm wheels, of which the
axes of any working or engaging pair are so placed at an angle one to the other
and in different planes, that the sliding of each in the direction of its axis causes a
different ratio of speed, or number of revolutions between the driving and driven
worm wheels, substantially as described and shewn.
3. A speed varying gear consisting of two or more worm wheels each of which
has its threads or teeth of increasing pite's or angle from one end to the other, so,
that in two or more such worm wheels working together, the sliding of each
simultaneously in the direction of its axis causes a different band of contact in each
wheel to be brought into working position, thus causing a different ratio of speed
or number of revolutions between the driving and driven wheels, substantially as
described and shewn.
4. A speed varying gear consisting of two or more worm wheels of which the
axes of any working or engaging pair are at an angle one to the other and in
different planes, combined with means for sliding them simultaneously each in the
direction of its own axis, substantially as described and shewn.
5. A speed varying gear having one or both of its increasing pitch worm wheels
grooved or divided circumferentially in the inanner and for the purpose shewn
and described with reference to Figs. 7 and 8.
6. A speed varying gear having one or both of its increasing pitch worm wheels
tapered to form truncated cones, in the manner and for the purpose shewn and
described with reference to Fig. 9.
7. A speed varying gear having one of its increasing pitch worm wheels formed
with a concave working surface, and the other with a convex working surface in
the manner and for the purpose shewn and described with reference to Fig. 10.
Dated this 27th day of November 1890.
WILLIAM J. MUNDEN.