Improvements in Variable Speed-gears, applicable for Use in the Propulsion of Tramcars and otherwise.
Year: 1894

page_text: Date of Application, 24th Apr., 1894.
Complete Specification Lelt, 24th. Jan., 1395-Accepted, 30th Mar., 1895
PROVISIONAL SPECIFICATION,
Improvements in Variable Speed-gears, applicable for Use in the
Propulsion of Tramcars and otherwise.
1, GEORGE GATTON MELHUISH HARDINGHAM, of 191, Fleet Street, in the
Courty of Middlesex, Civil Engineer, do hereby declare the nature of this
invention to be as follows :—
This invention relates to differential speed gears, and consists in means whereby,
from a driving shaft revolving at a uniform speed, different speeds may be
imparted to the driven shaft or drum without interfering with the engagement
of any of the toothed wheels intended to mesh with one another.
Means of the kind I am about to describe are applicable in the mechanical
propulsion of tramcars where the resistance varies considerably, to winches in
which a variation in the hoisting power is required, and under sundry other
circumstances where, with a given power and speed of driving shaft, an increased
load bas at times to be raised or resistance overcome without necessarily stopping
the apparatus for the purpose of bringing a different train of toothed gearing into
operation.
In the electric propulsion of tramears, it is of essential importance that the
motor run at its full normal speed, although the speed of the car may, owing to
abnormal resistance, be comparatively low. The difficulty in connection herewith
is peculiarly manifest at starting, the motor having to be many times more
powerful than is necessary for performing the average duty, the storage reservoirs
(where carried) having to be correspondingly increased in number, much additional
weight and expense being entailed.
In applying my invention, by way of example, to an electrically-propelled
tramcar and assuming that, at starting or on ascending a steep incline, it is desired
to increase the effective power of the motor four or five times-or in other words
to reduce the speed of the driven axle three-fourths or four-filths (as may be
desired) whilst the motor runs at its normal speed--1 introduce between the motor
shaft and the axle a duplex differential gear, preferably of the concentric type,
in which a central spur pinion is surrounded by an internally toothed wheel,
there being interposed between the central pinion and the surrounding wheel one
or more epicyclic wheels mounted upon a disc or upon a radial arm or arms
extending from a central hub mounted freely upon the central or pinion shaft.
In a differential gear adapted to accomplish the objects of the present invention,
the internally toothed wheel has two series of teeth respectively engaging with two
sets of intermediate wheels, and fast upon the central shaft are two pinions which
also respectively engage with the intermediate wheels. Each of the discs whereon
the intermediate wheels are mounted is provided with a friction strap attached to
a pivotted lever and capable of being tightened so as to hold stationary the disc
to which it is applied. When by these or other. suitable means, one of the discs
is held stationary, the intermediate wheel or wheels pertaining thereto is or are
rendered operative, the other disc meanwhile running. free and the intermediate
wheel or wheels mounted thereon remaining inoperative.
In order to provide for the considerable difference of speed requisite under the
conditions of working hereinbefore referred to (by way of example), the two trains
of gearing for communicating notion from the respective central pinions to the two
series of teeth of the internally toothed wheel are not only different but special in

page_text: character. For affording a low speed but high power, the pinion is of comparatively
small diameter, a single intermediate wheel or a set of intermediate wheels
communicating the motion direct from the said pinion to the internally toothed
wheel. For affording the high speed but low power, the intermediate gear is of
the compound type; that is to say, in place of each intermediate wheel two toothed
wheels of different sizes and rigidly connected together are used, the smaller of
these meshing with the central pinion and the larger one meshing with the
internally toothed wheel.
A duplex differential gear of the character described may be readily proportioned
in such a manner that when the high power is employed the internally toothed
wheel, whence the power is applied for driving the car, may be rotated at one-
fourth or one-fifth of the speed of the central pinion to which the
power derived
from the motor is applied. When, on the other hand, the high speed is employed,
the internally toothed wheel may be caused to rotate at the same speed as the
central pinion or thereabouts. Other proportions between the two speeds may,
however, obtain according to the necessities of the work to be accomplished; but
in any case, either the one or the other speed is rendered available by holding the
corresponding disc (carrying the intermediate wheel or wheels) stationary, without
interfering with the relative positions or meshing of any of the gear wheels.
Dated the 24th day of April 1894.
Improvements in Variable Speed-gears, applicable for Use in the
Propulsion of Tramcars and otherwise.
I, GEORGE GATTON MELHUISH HARDINGHAM, of 191, Fleet Street, in the
County of Middlesex, Civil 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 differential speed-gears, and consists in means whereby,
from a driving shaft revolving at a uniform speed, different speeds may be imparted
to the driven shalt without interfering with the engagement of any of the toothed
wheels intended to mesh with one another.
Means of the kind I am about to describe are applicable in the mechanical
propulsion of tramcars, where the resistance varies considerably, to winches
designed to work under a widely variable load, and under sundry other circum-
stances where, with a given power and speed of driving shaft, an increased
resistance has at times to be overcome without (in such a case as tramcar
propulsion) stopping the apparatus for the purpose of bringing a different train
of gearing into operation.
In the electrical propulsion of tramcars, it is of essential importance that the
motor run at its full normal speed, although the speed of the car may, owing to
abnormal resistance, be at times comparatively low. The difficulty in connection
herewith is peculiarly manifest at starting, the motor having to be of considerably
greater power than the ordinary duty demands and the storage reservoirs (where
carried) having to be correspondingly increased in number, much additional weight
and expense being entailed.
In applying my invention, by way of example, to an electrically-propelled
tramcar, and assuming that, at starting or on ascending a steep incline, it is desired
to increase the effective power of the motor four or five times-or, in other words,
to reduce the speed of the driven axle three-fourths or four-fifths (as may be
-desired), whilst the motor runs at its normal speed-I introduce between the
motor-shaft and the driven axle a duplex differential gear, preferably of the

page_text: concentric type, in which a central spur-pinion is surrounded by an internally-
toothed wheel, there being interposed between the central pinion and the
surrounding wheel, one or more epicyclic wheels carried upon a disc, or upon a
radial arm or arms, extending from a hub mounted freely upon the central or
pinion-shaft.
In the accompanying drawings is illustrated differential gear of the kind above
referred to, and a mode in which the same may be applied in the mechanical
propulsion of a tramcar;
Fig. 1 being a part side elevation and part longitudinal section, Fig. 2 a plan,
and Fig. 3 an end elevation.
Fig. 4 is a longitudinal section, to a larger scale, showing one inode of con-
structing the differential gear; Fig. 5 being a side elevation thereof.
Figs. 6 and 7 are views corresponding with Figs. 4 and 5 and illustrating an
alternative mode of constructing the differential gear.
Referring to Figs. 4 and 5, the internally-toothed and bi-part wheel A A¹ has
two series of teeth, respectively engaging with one or more intermediate wheels B
and B; and fast upon the central shalt S are two pinions C C. The pinion C₁
engages directly with the interinediate wheel or wheels B', whilst the pinion C
drives the intermediate wheel B through the intervention of the pinion B³,
both these latter being fast upon the axle d.
Each of the discs or drums D D',
in which are mounted the axles d d carrying the intermediate wheels B B',
is embraced by a friction-strap E (or E¹) attached to a lever such as F
pivoted at each such strap being capable of being tightened so as to hold
stationary the drum to which it is applied. (For the sake of simplicity of
illustration, the axles d dare shown singly, but it will be understood that
these, with their intermediate wheels, may be duplicated or triplicated.)
In order to provide for the considerable difference of speed requisite under
the conditions of working herein before referred to, the two trains of gearing
for communicating motion from the respective central pinions C C to the two
series of teeth of the internally-toothed wheel A A' are not merely differently
proportioned, but different in character. For affording a low speed but high
power, the pinion C¹ is of comparatively small diameter, an intermediate wheel B',
or a set of such wheels, communicating the motion directly from the said pinion Ci
to the internally-toothed wheel A'. For affording the high speed but low power,
the intermediate gear is of a compound type; that is to say, in place of each
intermediate wheel B', two toothed wheels B and B of different sizes and fast
on the same axle are used; the smaller of these B' meshing with the central
pinion C, and the larger one B meshing with the internally-toothed wheel A.
A gear of this description may be readily proportioned in such a manner that,
when the high power is employed, the internally-toothed wheel A' and the
pinion L, which is secured thereto and whence the power is applied for driving
the car, are rotated at about one-fourth or one-fifth of the speed of the shaft Š
to which the motion derived from the dynamo or other motor is applied, the
power varying in inverse ratio. When, on the other hand, the high speed is
employed, the internally-toothed wheel A may be caused to rotate at substantially
the same speed as the shaft S.
The proportions between the two sets of gear may, however, be varied, and
other relative speeds obtained, according to the necessities of the work to be
accomplished. Or, when a comparatively small difference between the speed<
afforded by the respective gears is required, the pinion B' may be dispensed with,
the pinion C arranged within the wheel A, and the intermediate wheel B arranged
to mesh with both, as in the gear-train C, B', A'. To render the difference of
speed between the pinion C and the internally-toothed wheel A small, the pinion C
is relatively to the wheel A as large and the intermediate wheel B as small as
convenient; whilst, to render the difference of speed large, the pinion C¹ is as small
and the intermediate wheel B' as large as convenient.
With any of these arrangements either the one or the other speed is rendered

page_text: available by tightening the strap about the one or the other of the drums D, D',
and thereby holding the bearings of the axles d or d' stationary; either the one
or the other train of gearing being. thus brought into operation without interfering.
with the relationship of any of the toothed wheels designed to mesh together.
According to another method of construction, illustrated in Figs. 6 and 7, instead
of the central pinions pertaining to both sets of gear being secured to the actuating
shaft, the central pinion belonging to one gear-train and the internally-toothed
wheel of the other gear-train are fast on the said shaft. Similarly, instead. of the
internally-toothed wheels pertaining to both sets of gear being in connection with
the pinion L, drum or pulley, whence the motion is yielded, the internally-toothed
heel belonging to one gear-train and the central pinion of the other gear-train are
in permanent 'connection with the pinion L. The intermediate wheels are carried
on axles mounted in discs or drums, as in the previous construction; each of these
drums being embraced by a friction-strap whereby it may be held stationary when
the set of gear to which it pertains is to become operative. Referring to the
drawing, S is the actuating shaft to which the central pinion C' and the internally-
toothed wheel A are secured; the central pinion C and the internally-toothed
wheel A being in connection with the pinion L. B B' are the intermediate wheels
mounted on axles d¹ carried. in drums D D', respectively embraced by the
friction-straps E E¹. These straps are attached to and are operated by pivoted
levers such as F, as previously described with reference to Figs. 4 and 5.
With duplex differential gear of the type last described; when the strap E is
tightened and the high speed gear is brought into operation, the rotative speed of
the pinion Lis greater than that of the, actuating shaft S. When, on the other
hand, the strap E' is tightened, and the high power gear is brought into operation,
the rotative speed of the pinion L is less than that of the actuating shaft S, and
(in a gear proportioned substantially as illustrated) is about one-fourth of that
previously prevailing, or yields about four times the, power. By increasing the
diameter of the pinions in proportion to that of the internally-toothed wheels, the
difference of effect obtainable is diminished. Although advantageous. in respect of
cost of manufacture, it is not essential that the pinions' C C, the intermediate
wheels B-B', or the internally-toothed wheels A A', should be respectively of
equal diameter.
One mode of applying my invention to a mechanically-propelled tramcar is
illustrated in Figs. 1, 2 and 3; this design embracing the form of differential gear
described with reference to Figs: 6 and 7. The means employed for working the
levers to which the straps E E' are attached, and whereby they are tightened
about their drums, comprise a lever G pivoted at H and furnished with
quadrants 99¹ to which chains or cords KK are attached; the latter passing over
and around guide pulleys and being respectively connected to the levers F and F.
The lever G is by preference formed in two parts, the upper part fitting into a
socket formed in the lower part, and capable of being readily removed and carried
to the opposite end of the car, there to be inserted in the socketed part provided at
that end. By moving the lever G in one direction, the strap E is tightened, the
drum D held stationary, and the intermediate wheel (or wheels) B rendered
serviceable as a fulcrum for communicating motion from the internally-toothed
wheel A to the pinion C and pinion L. Upon moving the lever G' in 'the opposite
direction, the drum D is released, the strap E' tightened,. the drum D held
stationary, and the intermediate wheel (or wheels) B' rendered serviceable for
communicating motion from the pinion C¹ to the internally-toothed wheel A! and
pinion L. The lever G may be secured in either extreme position by means of a
thumb-nut, catch or other locking device. Or the lever G may be set at
mid-stroke, in which case neither train of gear is operative.
It will thus be understood that, to obtain a high speed, it is merely necessary for
the strap E to be slackened and the strap E tightened; while, to obtain a high
power, the strap E is slackened and the strap E' tightened; the change from the
one speed to the other being accomplished without stopping the engine or

page_text: necessarily altering its speed, or interfering with the relative positions or meshing
of any of the gear-wheels. When employing an electric motor, it will nevertheless
be expedient to connect the quadrants gy', or other convenient part of the
controlling mechanism, with a switch, arranged in such a manner that, whilst the
hand-lever G is being moved from one extreme position to the opposite,
the current to the motor is momentarily interrupted. For a run down-hill, for
example, the hand-lever G would be set at mid-stroke, the straps E and E' would
both be slack, and the supply of current to the motor would be cut off.
Having now particularly described and ascertained the nature of this inveu-
tion and in what manner the same is to be performed, I claim :-
1. In the mechanical propulsion of tramcars and for other uses where it is
desired to vary the speed or power yielded whilst the speed of the motor or power-
shaft remains constant, the employment of duplex differential gear arranged or
operating substantially as described with reference to Figs. 4 and 5 of the
accompanying drawings.
2 In the mechanical propulsion of tramcars and for other uses where it is
desired to vary the speed or power yielded whilst the speed of the motor or power-
shaft remains constant, the employment of duplex differential gear arranged or
operating substantially as described with reference to Figs. 6 and 7 of the
accompanying drawings.
3. The improved duplex driving gear, adapted for use in the mechanical
propulsion of tramcars and for other purposes, comprising an internally-toothed
wheel, or pair of internally-toothed wheels, to which is connected the pinion,
drum or pulley, whence the motion is yielded, two central pinions fast on the
actuating shaft and respectively meshing with or otherwise operating two inter-
mediate wheels or sets of wheels, the latter meshing with the internally-toothed
wheel and being carried in discs or drums mounted to rotate freely on the central
shaft, the said drums being provided with friction-straps or equivalent means
whereby either the one or the other may be held stationary and the train of gear
pertaining thereto rendered operative, substantially as herein described.
4. The improved duplex driving gear adapted for use in the mechanical
propulsion of tramears and for other purposes, comprising an internally-toothed
wheel and a central pinion to which is connected the pinion, drum or pulley, whence
the motion is yielded, a central pinion and an internally-toothed wheel fast on the
actuating shaft, and two intermediate wheels or sets of wheels respectively meshing
with the central pinions and with the internally-toothed wheels, the said inter-
mediate wheels or sets of wheels being respectively carried in discs or drums
mounted to rotate freely on the central shaft, and the said drums being provided
with friction-straps or equivalent means whereby either the one or the other may
be held stationary and the train of gear pertaining thereto rendered operative,
substantially as herein described.
5. In a duplex differential driving gear comprising two gear-trains each
consisting of three elements, such as a central pinion, an intermediate wheel or set
of intermediate wheels carried on an axially mounted arm or arms, and a
surrounding internally-toothed wheel, rendering one of the elements of each gear-
train capable of being held stationary or of being released, according to whether
such gear-train is required to be operative or inoperative, substantially as herein
described.
Dated the 24th day of January 1895.
G. G. M. HARDINGHAM.