Improvements in Methods and Apparatus for Applying the Power of Electric Motors, especially applicable to Electric Railways.
Year: 1890

page_text: Date of Application, 11th July, 1890
Complete Specification Left, 7th Apr., 1891-Accepted, 6th June, 1891
PROVISIONAL SPECIFICATION.
Improvements in Methods and Apparatus for Applying the Power of
Electric Motors, especially applicable to Electric Railways.
I, BENJAMIN JOSEPH BARNARD MILLS, of 23 Southampton Buildings, in the.
County of Middlesex, Patent Agent, do hereby declare the nature of this invention,
a communication to me from abroad by Thomas Alva Edison, of Llewellyn Park,
in the County of Essex, and State of New Jersey, in the United States of America,
Inventor, to be as follows:-
The object of this invention is to produce an improved method and apparatus for
the economical operation of machinery of all kinds by electric motors, and especially
machinery of that character which it is desired to vary in speed and to reverse in
direction. The invention is especially applicable to the propulsion of moving
vehicles, such as tram cars and the like, for which use it has especial advantages,
but it is also applicable to the running of elevators and also, as before indicated, to
the driving of all classes of machinery. It designed to secure the desired
variations in speed and direction of rotation without the utilization of energy
wasting devices.
In one form of the apparatus, two similar electric motors are employed, and
these are connected with the shaft to be driven by differential gearing, which may
be composed of two wheels mounted loosely upon the shaft to be driven, and an
intermediate wheel or wheels mounted upon an arm fixed to the shaft and turning
therewith. The intermediate wheels have the capacity to rotate upon their own
axes as well as to turn around with the shaft. The two electric motors are
connected with and turn the two loose wheels of the differential gearing. With a
simple form of the gearing, the rotation of the motors and the loose wheels of the
gearing, with equal speed in opposite directions, will cause the intermediate wheels
to simply rotate upon their axes without exerting any rotary effort upon the shaft.
If one motor runs faster than the other, the intermediate wheels will not only rotate
upon their own axes; but will turn the shaft with a speed equal to one half of the
difference in the speed of the two motors, and in the direction of the faster motor.
Thus the driven shaft can be stopped or run in either direction and its speed
increased or decreased without stopping the motors or changing their directions of
rotation.
The difference in the speed of the two motors may be accomplished in any of the
ways known to electricians for changing the speed of electric motors without the
employment of energy wasting devices. A convenient method to employ is that of
changing the strength of the field magnets of the machines. Considering the two
machines as A and B, the conditions of operation may be stated as follows:-When
the field magnets of A and B are of the same strength, both machines will be
driven as motors at the same speed and the shaft will be at rest. When the field
of A is weaker than that of B, the machine A will run faster than the machine B,
and the driven shaft will turn in the same direction as A; under these conditions,
and assuming a sufficient load, the machine A will act as a motor, while the
machine B, since it receives the thrust of the machine A will act as a dynamo
generating a current which is delivered to the machine A. When the field of B is
weaker than that of A, the reverse conditions will be present; the machine B
will act as a motor and will run faster than the machine A which will act as a
dynamo, while the rotation of the driven shaft will now be in the same direction as
that of the machine B. Thus the driven shaft is varied in its speed and direction
of rotation by changing the speed and dynamic relations of the two motors,

page_text: The machine acting for the time as a dynamo, delivers its current to the machine
acting for the time as a motor, while additional current is taken from the source to
supply the latter machine. Thus the energy expended upon the machine acting as
a dynamo is re-delivered, less the loss due to conversion, to the motor for the
performance of useful work, and an economical arrangement is produced.
In the application of the invention to the propulsion of vehicles such as tram cars,
an additional condition will be introduced, if it is desired to stop the car while
maintaining the circuit connections of the machines. While the car is being driven
forward by its momentum, the dynamic conditions of the two machines will be
reversed from what they are required to be to drive the car in the same direction,
and although one machine still acts as a motor and the other as a dynamo, the dynamo
may generate more current than will be taken by the motor, and the result may be
the delivering of current back to the line.
The armatures of the electric motors may be sleeved directly upon the driven
shaft, and the loose wheels of the gearing may be carried upon the same sleeves, or
the armatures may be mounted upon separate shafts and be connected with the loose
wheels by gears, belts, chains, or other means.
A convenient arrangement for controlling the two motors is to provide an
adjustable resistance which by means of a switch arın may be simultaneously
removed from the field circuit of one machine, and introduced into that of the other
machine, and vice versa, so that by the simple forward and backward movement of
this single switch arm, the entire operation of the machines will be performed, and.
all the conditions before referred to produced.
The differential gearing may be composed of cog wheels as is usual, but a special
construction of such gearing has been devised and forms a part of this invention,
whereby the loose wheels of the train are connected with the intermediate wheels by
one or more endless belts, chains, or ropes. This is accomplished by providing the
arm projecting from the shaft between the loose wheels with a cross bar, upon
the ends of which are mounted two wheels, which are placed tangential to and on the
same side of the loose wheels. An endless belt, chain, or rope passes vertically over
one loose wheel, then horizontally around one of the interinediate wheels and
vertically over the other loose wheel and then horizontally around the second
intermediate wheel and back to the point of starting. In order that the two loose
wheels may be made to produce the results desired when revolving in the same
direction rather than in opposite directions (a construction which has advantages for
some uses) an additional intermediate element may be introduced into the gearing.
This additional intermediate element may be two similar intermediate wheels on the
other side of the loose wheels and mounted on a cross bar on the end of an
extension of the shaft arm on the other side of the shaft. The endless belt, chain,
or rope, is turned around these additional wheels and its direction on one of the
louse wheels is thereby reversed, thus causing these loose wheels to produce, when
turned in the same direction, the same results that they did in the first form
described when turned in opposite directions. To enable the employment of two or
more endless belts, chains, or ropes, with the same differential gearing, a desirable
thing to do when ropes or belts, which may slip, are employed, additional wheels of
sinaller size are used, placed within the larger wheels and secured to them, so that
they turn altogether as one. A shorter endless belt or rope passes over each set of
these smaller wheels. When an endless chain is employed to connect the wheels
of the differential gearing, the wheels will be constructed to conform to the shape of
the chain, so that all slipping will be avoided. The chain will be made of steel to
prevent stretching.
In another forin of the apparatus, only one electric motor is employed, both loose
wheels of the differential gearing being driven from this one motor by means of
endless belts, ropes, chains, or the like. The connection of the motor with one of
the loose wheels of the differential gearing is made through any suitable device for
changing the ratio of transmission. For this purpose there may be employed an
endless rope, belt or chain passing over two expanding pulleys which are adjusted

page_text: simultaneously in opposite directions by suitable mechanism, i.e., one pulley is made
smaller in diameter while the other is made larger and in the same degree. When
the same speed relations exist between the motor and both sides of the differential
gearing, the loose wheels will be revolved with the same speed and the driven shaft
will be at rest. By adjusting the expanding pulleys, the loose wheel on that side of
the train can be made to revolve faster or slower than the loose wheel on the other
side of the train, and the driven shaft can thus be turned in either direction. It
will be seen that by this form of the apparatus the shaft can be stopped or rotated
in either direction and with a speed varying from the minimum to the maximum, by
simply adjusting the speed relations between the motor and one side of the
differential gearing by means of the expanding pulleys or any other suitable device
performing the same functions which may be provided for the purpose. The
variations in speed and direction of rotation will be effected in this form of the
apparatus as well as in the form first described without wasting of energy.
The expanding pulleys may be of various constructions. One form is composed
of a movable and a stationary head or disc connected by a rope running through
smooth holes in the periphery of the heads or discs and across from one head or disc
to the other, thus forming a flexible bearing surface for the endless rope or belt
which transmits motion from one pulley to the other. The strain of the endless
belt or rope will cause the pulley rope to draw through the holes and give the
pulley the proper diameter for the particular adjustment of the movable head
or disc.
Another form is composed of two sets of bars arranged upon a drum and having
teeth similar to saw teeth. The bars of one set alternate with those of the other
set and have their teeth set with the inclines facing those of the other set. The
bars of one set are stationary while those of the other set are movable, sliding in
and out, so that the grooves formed between the teeth of the two sets of bars in
which endless ropes or chains work are increased or diminished in diameter.
Instead of the expanding pulleys, any other suitable device for changing the ratio
of transmission between the motor and one side of the differential gearing may be
employed.
1
1
1000
COMPLETE SPECIFICATION.
Improvements in Methods and Apparatus for Applying the Power of
Electric Motors, especially applicable to Electric Railways.
I, BENJAMIN JOSEPH BARNARD MILLS of 23 Southampton Buildings in the
County of Middlesex Patent Agent do hereby declare the nature of this inven-
tion, a communication to me from abroad by Thomas Alva Edison of Llewellyn
Park in the County of Essex and State of New Jersey in the United States of
America, Inventor, and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement:-
The object of this invention is to produce an improved method and apparatus for
the economical operation of machinery of all kinds by electric motors, and especially
machinery of that character which it is desired to vary in speed and to reverse in
direction. The invention is especially applicable to the propulsion of moving
vehicles, such as tram cars and the like, for which use it has especial advantages,
but it is also applicable to the running of elevators, and also, as before indicated, to
the driving of all classes of machinery. It is designed to secure the desired
variations in speed and direction of rotation without the utilization of energy-
wasting devices.
In one form of the apparatus, two similar electric motors are employed and these

page_text: are connected with the shaft to be driven by differential gearing, which may be
composed of two wheels mounted loosely upon the shaft to be driven and an inter-
mediate wheel or wheels mounted upon an arm fixed to the shaft and turning
therewith. The intermediate wheels have the capacity to rotate upon their own
axes as well as to turn around with the shaft. The two electric motors are
connected with and turn the two loose wheels of the differential gearing. With a
simple form of the gearing, the rotation of the motors and the loose wheels of the
gearing with equal speed in opposite directions, will cause the intermediate wheels
to simply rotate upon their axes without exerting any rotary effort upon the shaft.
If one motor runs faster than the other, the intermediate wheels will not only rotate
upon their own axes but will turn the shaft with a speed equal to one half of the
difference in the speed of the two motors and in the direction of the faster motor.
Thus the driven shaft can be stopped or run in either direction and its speed
increased or decreased without stopping the motors or changing their directions of
rotation.
The difference in the speed of the two motors may be accomplished in any of the
ways known to electricians for changing the speed of electric motors without the
employment of energy-wasting devices. A convenient method to employ is that of
changing the strength of the field magnets of the machines. Considering the two
machines as A and B the conditions of operation may be stated as follows:-When
the field magnets of A and B are of the same strength both machines will be
driven as motors at the same speed and the shaft will be at rest. When the field
of A is weaker than that of B, the machine A will run faster than the machine B
and the driven shaft will turn in the same direction as A; under these conditions
and assuming a sufficient load, the machine A will act as a motor while the
machine B, since it receives the thrust of the machine A, will act as a dynaino
generating a current which is delivered to the machine A, When the field of B is
weaker than that of A, the reverse conditions will be present; the machine B will
act as a motor and will run faster than the machine A which will act as a dynamo
while the rotation of the driven shaft will now be in the same direction as that of
the machine B. Thus the driven shaft is varied in its speed and direction of
rotation by changing the speed and dynamic relations of the two motors.
The machine acting for the time as a dynamo delivers its current to the machine
acting for the time as a motor, while additional current is taken from the source to
supply the latter machine. Thus the energy expended upon the machine acting as
a dyuamo is redelivered, less the loss due to conversion, to the motor for the
performance of useful work, and an economical arrangement is produced.
In the application of the invention to the propulsion of vehicles such as tram
cars, an additional condition will be introduced, if it is desired to stop the car while
maintaining the circuit connections of the machines. While the car is being driven
forward by its momentum, the dynamic conditions of the two machines will be
reversed from what they are required to be to drive the car in the same direction
and although one machine still acts as a motor and the other as a dynamo, the
dynamo may generate more current than will be taken by the motor and the result
may be the delivering of current back to the line.
The armatures of the electric motors may be sleeved directly upon the driven
shaft and the loose wheels of the gearing may be carried upon the same sleeves, or
the armatures may be mounted upon separate shafts and be connected with the
loose wheels by gears belts chains or other means.
A convenient arrangement for controlling the two motors is to provide an
adjustable resistance, which by means of a switch arm may be simultaneously
removed from the field circuit of one machine and introduced into that of the other
machine and vice versa, so that by the simple forward and backward movement of
this single switch arm the entire operation of the machines will be performed and all
the conditions before referred to produced.
The differential gearing may be composed of cog wheels as is usual but a special
construction of such gearing has been devised and forms a part of this invention,

page_text: whereby the loose wheels of the train are connected with the intermediate wheels
by one or more endless belts, chains or ropes. This is accomplished by providing the
arm projecting from the shaft between the loose wheels with a cross bar upon
the ends of which are mounted two wheels which are placed tangential to and on
the same side of the loose wheels. An endless belt chain or rope passes vertically
over one loose wheel, then horizontally around one of the intermediate wheels and
vertically over the other loose wheel and then horizontally around the second
intermediate wheel and back to the point of starting. In order that the two loose
wheels may be made to produce the results desired when revolving in the same
direction rather than in opposite directions (a construction which has advantages for
some uses) an additional intermediate element may be introduced into the gearing.
This additional intermediate element may be two similar intermediate wheels on the
other side of the loose wheels and mounted on a cross bar on the end of an extension
of the shaft arm on the other side of the shaft. The endless belt chain or rope is
turned around these additional wheels and its direction on one of the loose wheels is
thereby reversed, thus causing these loose wheels to produce when turned in the
same direction the same results that they did in the first form described when turned
in opposite directions. To enable the employment of two or more endless belts,
chains or ropes with the same differential gearing, a desirable thing to do when
ropes or belts which may slip are employed, additional wheels of smaller size are
used placed within the larger wheels and secured to them so that they turn together
as one. A shorter endless belt or rope passes over each set of these smaller wheels.
When an endless chain is employed to connect the wheels of the differential gearing
the wheels will be constructed to conform to 'the shape of the chain so that all
slipping will be avoided. The chain will be made of steel to prevent stretching.
In another form of the apparatus only one electric motor is employed, both loose
wheels of the differential gearing being driven from this one motor by means of
endless belts ropes chains or the like. The connection of the motor with one of the
loose wheels of the differential gearing is made through any suitable device for
changing the ratio of transmission. For this purpose there may be employed an
endless rope belt or chain passing over two expanding pulleys which are adjusted
simultaneously in opposite directions by suitable mechanism i.e. one pulley is made
smaller in diameter while the other is made larger and in the same degree. When
the same speed relations exist between the motor and both sides of the differential
gearing, the loose wheels will be revolved with the same speed and the driven shaft
will be at rest. By adjusting the expanding pulleys the loose wheel on that side of
the train can be made to revolve faster or slower than the loose wheel on the other
side of the train and the driven shaft can thus be turned in either direction. It
will be seen that by this form of the apparatus the shaft can be stopped or rotated
in either direction and with a speed varying from the minimum to the maximum,
by simply adjusting the speed relations. between the motor and one side of the
differential gearing by means of the expanding pulleys or any other suitable device
performing the same functions which may be provided for the purpose. The
variations in speed and direction of rotation will be effected in this form of the
apparatus, as well as in the form first described, without wasting of energy.
The expanding pulleys may be of various constructions. One form is composed
of a movable and a stationary bead or disc connected by a rope running through
smooth holes in the periphery of the heads or discs and across from one head or
disc to the other thus forming a flexible bearing surface for the endless rope or belt
which transmits motion from one pulley to the other. The strain of the endless
belt or rope will cause the pulley rope to draw through the holes and give the
pulley the proper diameter for the particular adjustment of the movable head
or disc.
Another form is composed of two sets of bars arranged upon a drum and having
teeth similar to saw teeth. The bars of one set alternate with those of the other
set and have their teeth set with the inclines facing those of the other set. The

page_text: bars of one set are stationary while those of the other set are movable, sliding in
and out so that the grooves formed between the teeth of the two sets of bars in
which endless ropes or chains work, are increased or diminished in diameter.
Instead of the expanding pulleys, any other suitable device for changing the
ratio of transmission between the motor and one side of the differential gearing may
be employed.
In the accompanying drawings
Figure 1. is a view of two motor armatures and connecting gearing with a
diagram of circuits, for the illustration of the conditions of operation of one form of
the apparatus.
Figure 2. is a top view (with a diagram of one form of the electrical connections)
illustrating the driving of a shaft which may be connected by any suitable means
with the machinery to be driven.
Figure 3. is a top view illustrating one way of applying the apparatus to
tram cars.
Figure 4. is a perspective view of a simple form of the improved differential
gearing with endless rope or chain connections between the wheels.
Figure 5 is a view similar to Figure 4 of a form of the improved differential
gearing in which the differentially acting wheels rotate in the same direction.
Figure 6. is a top view showing the employment of a plurality of ropes or chains
with the differential gearing.
Figures 7 and 8 are views on a larger scale showing the wheel construction of
the differential gearing when an endless chain is employed.
Figure 9. is a top view illustrating another way of applying the apparatus to the
propulsion of tram cars.
Figures 10 and 11 are perspective views of a simple form of the improved
expanding pulley having a rope bearing surface.
Figures 12 and 13 are views of a compound expanding pulley constructed with a
rope bearing surface; and
Figure 14 is a sectional view of another form of expanding pulley.
Referring to Figure 1. A and B are the armatures of two similar electric
motors which turn in opposite directions as shown by the arrows 1. These
armatures are sleeved upon the shaft, C, and are connected together and with the
shaft by a differential gearing, D, E, F. The wheel, D, is carried by the
armature A, the wheel E by the armature, B, and the intermediate wheel F is
mounted upon an arm fixed to the shaft C between the loose wheels D, E. The
armatures are connected with a line circuit + When the field magnets of A
1
and B are of the same strength, both machines will be driven as motors at the same
speed and the shaft will be at rest. When the field of A is weaker than that of B,
the machine A will run faster than the machine B and the driven shaft C will turn
in the same direction as A as shown by the arrow 2: under these conditions and
assuming a sufficient load upon the machines, the machine A will act as a motor
while the machine B, since it receives the thrust of the machine A, will act as a
dynamo generating a current which is delivered to the machine A and the flow of
electric current will be as indicated by the arrows 3. When the field of B is
weaker than that of A, the reverse conditions will be present: the machine B will
act as a motor and will run faster than the machine A which will act as a dynamo,
while the rotation of the driven shaft C will now be in the same direction as that
of the machine B, as shown by the arrow 4 while the flow of the electric current
will be as indicated by the arrows 5. Thus the driven shaft C has its speed and
direction of rotation changed, by changing the speed and dynamic relations of the
two motors, and this is accomplished without wasting energy. If the apparatus is
applied to a tram car and the machines A and B are adjusted electrically for the
same speed while the car is in motion, the momentum of the car will drive the
apparatus and for a limited time current may be returned to the line as indicated
by the arrows 6. If while the car is running in the direction of arrow 2 the

page_text: machines are adjusted electrically so as to tend to come to the same speed, and
the car is carried forward a further distance by its momentum, the machine A
will become a dynamo and the machine B will become a motor and the currents
through the machines themselves will be as shown by the arrows 5 instead of as
shown by the arrows 3. which represent the flow of current through the machines
themselves while they are driving the car in the same direction; while current
may flow back upon the line as shown by the arrows 6. If the machines are
adjusted for equal speed while driving the car in the direction of arrow 4 the
machine B, will while the car is carried forward by its momentum, act as a
dynamo, the machine A will act as a motor, the current through the machines
themselves will flow as indicated by the arrows 3, while current may be delivered
back to the line as indicated by arrows 6. In this way the machines can be used
if desired to brake the car or to assist in that operation, since instead of adjusting
them for equal speeds, when it is desired to brake the car, they can be adjusted to
any extent for the reverse relation of their speeds.
Referring to Figure 2. C is the driving shaft, A and B are the two motors
and D, E, and F represent the differential gearing. A gear wheel G is shown for
transmitting the power developed, but any device may be used for the purpose.
The main current supplying the circuit is indicated by the signs + and By
the method of connection shown in Figure 2, the motor armatures are connected in
multiple are with this circuit + and so are the Geld magnets.
A resistance H is located in the field circuits of the two machines A B. This
resistance is adjusted by means of a switch, I, in such manner that the portion of
the resistance on the right of the switch, I, is in the field circuit of the machine B,
while the portion of the resistance on the left of the switch I is in the field circuit
of the machine A. The shifting of the switch to the left diminishes the resistance
in the field of the machine A and increases that in the field of the machine B.
A movement to the right produces the reverse effect. If the switch I stands at a
central position, making the resistance in the two field circuits equal, the two
machines will have an equal speed in opposite directions, and the shaft C will
remain at rest. By throwing the switch I to the left the field magnet of the
machine A is strengthened while that of the machine B will be weakened resulting
in the conditions illustrated by the arrows 4 and 5 in Figure 1. before referred to,
and producing a rotation of the shaft C at a speed which is equal to one half of the
difference in the speed of the two machines, and which may be varied within wide
limits. By swinging the switch I to the right the field of the machine B will be
made strong and that of the machine A weak, and the conditions illustrated by the
arrows 2 and 3 in Figure 1 will be obtained. The changing of the speed and
dynamic relations of the two machines by adjusting the strength of the field
magnets produces the desired variations in speed and direction of rotation of the
driven shaft without the wasting of energy.
Referring to Figure 3. The two motors A and B are shown as multi-polar
machines although any type of electric motor may be employed. These machines
are hung upon the axles C C¹ of the tram car. The wheels D, E, F of the
differential gearing which are mounted on the axle C are connected together by an
endless chain a, a construction which will be fully hereinafter explained. The
loose wheels D, E, of the gearing are secured to gear wheels D₁ E' which are
engaged by pinions d, e, on the arinature shafts of the motors. The connections
between the motors and the wheels D E may be made by endless chains, ropes or
belts instead of by cog wheels.
Referring to Figures 4, 5, 6, 7, and 8. The improved form of differential
gearing which forms one of the features of the invention, is one employing trans-
mitting endless ropes, belts or chains instead of engaging cogs. In its simplest
form (Figure 4) it is composed of two wheels A, B, mounted loosely on a shaft C
and rotating in parallel planes. Between the wheels there projects from the shaft
an arm a which is fixed to the shaft and has at its outer end a cross bar which
'

page_text: carries two wheels E F.
These wheels EF are thus located on one side of the
centre of the wheels A B and are tangential thereto. An endless rope belt or
chain G passes around the wheels A B and E F as shown.
Assuming that power is applied to the wheels A B so as to produce rotation of
such wheels in opposite directions as shown by the arrows in Figure 4; if the
wheels A, B, rotate with the same speed the wheels E F will turn but the shaft C
will remain at rest. Now if the wheel A rotates faster than the wheel B the belt
speed of the latter will be less than of the former and the latter will not supply the
rope or belt fast enough for the former, and the arm a, will be carried around in
the same direction as that in which the wheel A rotates with a speed equal to one
half of the difference in speed between the wheels A and B and thus the shaft C
will be turned. If the wheel B rotates faster than the wheel A, the direction of
rotation of the shaft C will be reversed and its speed of rotation will be equal to
one-half of the difference in speed between the two wheels.
This form of differential gearing produces all the effects of a similar gearing with
cog wheels such as shown in Figures 1 and 2 whether the power is applied to
the wheels or to the shaft, and when applied to the former whether it operates
one or both wheels and in the latter case whether the wheels turn in the same
or in opposite directions. The gearing with belt rope or chain connected wheels
can be run at a higher speed than one with cog wheels, produces little noise and
is more practical gearing in many ways. Like the differential gearing composed
of cog wheels it may be used in all the ways indicated or in any other manner
within the range of its utility.
To revolve the wheels A and B of Figure 4 in opposite directions from a shaft
would require the use of a crossed belt for one of the wheels, or an intermediate cog
wheel if cog wheels were employed for the connections. In the form of the
improved differential gearing shown in Figure 5, the wheels A B when rotated in
the same direction produce the same effects as when the wheels A B of Figure 4 are
rotated in opposite directions. This is accomplished by reversing the application
of the rope belt or chain G to one of the wheels A or B by the intervention of an
additional pair of intermediate wheels E¹ F1 which are mounted on the cross bar b¹
of an arin a projecting from the shaft C in line with the arm a, but in the
diametrically opposite direction. The additional pair of intermediate wheels forms
an additional element in the connection between the main wheels having the effect
of reversing the direction of rotation as does an additional wheel when introduced
into a simple train. When the wheels A and B of Figure 5 rotate with equal
speed in the same direction as indicated by the arrow the shaft C remains at rest;
if the wheel A revolves faster than the wheel B (the rope belt or chain being
reversed on the wheel A) the shaft C will rotate in the direction reverse to the
rotation of the wheel A; if the wheel B is the faster, the shaft C will rotate in the
same direction as the wheels. It will be seen that since the direction of travel of
the rope belt or chain G is reversed on the wheel A, one wheel A or B will only
give rope to the other when they are rotating in the same direction or with unequal
speed in opposite directions. If the wheels A and B of Figure 5 were rotated with the
same speed in opposite directions, one would not deliver any rope to the other and
the shaft C would revolve with a positive speed equal to that of the wheels. With
the arrangement of Figure 4, this only can happen when the wheels A and B are
rotated with equal speed in the same direction.
When made either in the simpler or more complex form, the differential gearing
may be provided with a plurality of ropes, chains or belts in order to give sufficient
tractive surface for the transmission of the power. This may be conveniently
accomplished, as illustrated in Figure 6 by the employment of additional main and
intermediate wheels H, I, of smaller diameter placed within the larger wheels.
this way as many ropes, belts or chains as desired may be employed. When an
endless chain is employed to connect the wheels of the differential gearing, the
peripheries of the wheels will be constructed with sockets and a central groove to
In

page_text: receive the links and prevent slipping, as shown in Figures 7 and 8, and the links
of the chain will be made of steel to prevent stretching.
Referring to Figure 9. Another form of the apparatus, in which the two sides of
the differential gearing. are driven from the same electric motor is shown in this
The
figure, C is the car axle or other driven shaft; K, K, are the car wheels.
differential gearing is mounted directly upon the car axle. The wheel A is secured
to a sleeve c upon which is also a pulley M, while the wheel B is upon a sleeve d
provided with a pulley N. O, is the electric motor mounted upon the car or upon
its truck in any suitable way and having pulleys PQ upon its armature shaft con-
nected by ropes or belts e, f, with the pulleys M, N. The pulleys M and P are
expanding pulleys which are adjusted simultaneously in opposite directions by a
centrally pivoted bar R moved by the driver of the car by means of an endless
chain and sprocket wheels one of which is upon the pivot of the bar R, and the
other upon a vertical shaft having a crank handle within reach of the driver.
By means of the expanding pulleys, or any other device performing the same
functions, the speed of the wheel A can be changed so as to be greater or less than
that of the wheel B, and the driven shaft can be varied in speed and direction of
rotation without the wasting of energy.
If the simpler form of the differential gearing such as shown in Figure 4 were
employed, one of the belts e orf would need to be a crossed belt. Since for rail-
road work and possibly for other uses, some device would be required to prevent
wearing of the ropes where they cross, the form of differential gearing having the
main wheels rotating in the same direction is preferred. That form is illustrated in
Figure 9 and both belts e and f are shown as direct belts. The gearing is made to
accomplish all the operations of starting the car slowly and running it in either
direction by the movement of the pivoted bar R and the adjustment thereby of the
pulleys M, P, by which the speed relations of the main wheels of the differential
gearing are changed. Any other device than the expanding pulleys which will
change the ratio of transmission between the motor and one side of the differential
gearing may be employed.
Referring to Figures 10, 11, 12, and 13. These figures show a construction for
the expanding pulleys to be used in connection with the arrangement of the
apparatus shown in Figure 9. S (Figures 10 and 11) is a disc fixed against
sliding movement, and T is a sliding disc adapted to be moved by the arm R.
These discs are provided near their periphery with smooth holes through which is
threaded a rope U, the ends of which are suitably fastened. As the sliding disc T
is moved towards the fixed disc S, the strain of the endless belt will take up the
slack in the pulley rope U and cause the pulley to act as if of a definitely smaller
size as shown in Figure 11. If a pulley adapted to carry two ropes or belts is
required, the same construction can be employed, as shown in Figures 12 and 13 in
which an additional fixed disc S¹ is used placed between the discs S and T and
having holes through which the rope U passes. As the sliding disc T, is moved
towards the middle fixed disc St the pulley rope will be drawn through the holes
in this disc S₁ by the strain of the driving belt and the contracted pulley will
appear as in Figure 13. It is evident that the same result could be obtained by
other relative movements of the disks, such as by rotating the disc T instead of
sliding it.
Referring to Figure 14. Another construction for the expanding pulley is shown
in this figure. It is composed of two sets N, O of plates provided with teeth
bevelled on one side. The plates N are secured at their outer ends to a disc or
head P which is fixed to the shaft, and at their inner ends to a collar Q. The
plates are secured to a disc or head R and a collar T which slide upon the shaft.
The plates N and O alternate about the shaft and together form a complete toothed
pulley with the alternating teeth movable. In the position shown in Figure 14 the
rope belts d are worked upon the smallest diameter. By sliding the bead R
inwardly the movable inclines h will push the ropes up the fixed incliues i and the

page_text: diameter of the pulley will be increased. A bushing upon the shaft may be used
as a support for the plates N, O.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is.
1. The method of operating electric motors, consisting in the employment of two
motors and causing such motors to act differentially upon the driven shaft and varying
the speed and direction of rotation of said shaft by changing the speed and dynamic
relations of such motors, without the employment of energy-wasting devices, sub-
stantially as herein before specified in connection with Figure 1 of the drawings.
2. The combination with a driven shaft, of two electro-dynamic or dynamo-
electric machines, differential gearing connecting such machines with the shaft, and
means for simultaneously increasing the strength of the field magnet of one machine
and decreasing the strength of the field magnet of the other machine, substantially
as set forth.
3. The combination of electric motors and connecting gearing substantially as
herein before specified, and as illustrated in Figures 1, 2 and 3 of the drawings.
4. In power transmitting apparatus, differential gearing having a belt, rope, or
chain connections between its wheels, substantially as set forth.
5. In power transmitting apparatus, a differential gearing having, in combination
with main belt, rope or chain wheels rotating in parallel planes and turning loosely
upon a shaft, of intermediate belt, rope or chain wheels mounted on an arm fixed to
the shaft and placed tangential to the main wheels, and an endless belt, rope or
chain passing around the main wheels and the intermediate wheels, substantially as
set forth.
6. In power transmitting apparatus, a differential gearing having belt, rope or
chain connections between its wheels and provided with additional intermediate
wheels, so as to permit the main wheels of the gearing to rotate in the same
direction, substantially as set forth.
7. In power transmitting apparatus involving the use of a differential gearing
having belt connections between the wheels, the combination of a plurality of belts
and corresponding sets of wheels, the wheels of the two or more sets being of
different sizes, with the smaller wheels located within the larger wheels, substan-
tially as set forth.
8. The differential gearing with belt, rope, or chain connected wheels, sub-
stantially as herein before specified and as illustrated in Figures 4, 5, 6, 7 and 8 of
the drawings.
9. The method of driving machinery by an electric motor and varying the speed
and reversing the direction of the driven machine independently of the speed and
direction of the electric motor and without the wasting of energy, consisting in
applying the power from the motor to two sides of a differential gearing and vary-
ing the speed relations between the motor and the differential gearing, substantially
as set forth.
10. The combination with a driven shaft and a differential gearing, of an electric
motor, connections between the electric motor and the opposite sides of the
differential gearing, one of such connections being made through a device for
varying the ratio of transmission, so as to change the speed relations between
the electric motor and one side of the differential gearing, substantially as set
forth.
11. The combination of an electric motor and connecting gearing substantially
as herein before specified, and as illustrated in Figure 9 of the drawings.
12. In power transmitting apparatus, an expanding pulley having relatively
moveable heads or discs and a flexible connection between the discs upon which
the belt travels and which is made smaller or larger by the relative movement of
the discs, substantially as set forth.

page_text: 13. The expanding pulleys substantially as hereinbefore specified and as illas-
trated in Figures 10, 11, 12 and 13 of the drawings.
14. The expanding pulley composed of relatively movable toothed bars, sub-
stantially as herein before specified and as illustrated in Figure 14 of the drawings.
Dated CHS vu uay v
B. J. B. MILLS.
By Harris & Mills,
23, Southampton Buildings, London, Agents.