Improvements in or in connection with an Electric Motive Power System.
Year: 1892

page_text: Date of Application, 2nd Dec., 1892
Complete Specification Left, 26th Aug., 1893-Accepted, 30th Sept., 1893
PROVISIONAL SPECIFICATION.
Improvements in or in connection with an Electric Motive
Power System.
WILFRID L. SPENCE and D. STEWART & COMPANY, LIMITED, of The London
Road Iron Works, Glasgow, Civil and Mechanical Engineers, respectively, do
hereby declare the nature of this invention to be as follows:-
-
This invention relates more particularly to an electric rail or tramway system,
but it is also applicable, in part, to other purposes.
Hitherto shunt wound motors have invariably been found a failure on electric
locomotives. We use shunt wound motors by preference and overcome all
objections to their use by the following means or some of them.
(1) In the field circuit is placed an automatic switch to cut off the armature
current whenever the exciting current is by any means reduced below a pre-
determined minimum. Thus the E.M.F. can never be across the armature terminals
in an unexcited field.
(2) Once the automatic switch in (1) has opened the main circuit it can only
be replaced when the armature circuit is broken. The motions being locked.
(3) A separate earth connection, by wire brush or otherwise, is provided for the
shunt current and this circuit is connected direct to the trolley or collector and not
to the armature terminals.
(4) Each wheel axle is driven, through an electro-magnetic clutch gear, by a
connecting rod and crank pin from the motor spindle.
(5) One motor only, connected to both axles, is used by preference. This motor
may, and should, be smaller than either of the two motors on a similar car driven
in the usual way by toothed gearing.
(6) The motor runs constantly in one direction at one speed independently of the
motion of the car or train.
(7) Variable speed reduction: A system of electric contacts and tripping gear
permits of the clutch in (4) holding only through any desired distance; during the
remainder of the travel, which is constant, it is inoperative.
(8) A spring transforms the jerky motion of the clutch gear into a uniform one
on the wheel axle.
(9) A friction, electro-magnetic, or pawl and ratchet brake which holds only
when the driving clutch is free, prevents the spring in (8) causing the clutch drum
to run back.
(10) Reversal is obtained by causing the clutch to hold ou the return stroke
instead of on the forward one.
(11) The driver's regulating handle controls only the position of the tripping
gear in (7). It does not affect the main current at all directly, which is self-
regulating in proportion to the work done.
(12) No resistances are ordinarily used either in the armature or shunt circuits,
nor is any altering of field connections necessary or desirable. In altogether
exceptional cases both methods may be used as an additional means of speed
regulation.
(13) Alternate current motors, whether synchronising or not, are equally
applicable with direct current machines. This arises from the fact that, under
normal conditions, the motor is never stopped, it simply runs free when the car is
being slowed down or is standing.
(14) The exciting current may be provided by batteries, through a commutator,
or otherwise; the former method has the advantage that the cars may be lit with
non-fluctuating lamps.

page_text: In order to facilitate rapid gripping and release by the clutch the exciting coils
must be wound to reduce, as far as possible, the "time constant," the winding
moreover should be of such a nature as to minimise sparking; and the magnetic
circuit in addition to being laminated throughout should have another break besides
the two air gaps. A very convenient construction of the outer part carrying the
coils the inner drum is better without any direct magnetisation-is to form it of,
say, 24 separate poles each with a yoke at the back completing the circuit, through
a very short air space, to the adjacent portions. If the radial depth of the yoke
is made equal to the available length of limb the whole of the stampings necessary
may be cut from straight strips without waste. The two portions of the clutch-
driving and driven-should approach as closely as possible together without actual
contact.
It is desirable that the clutch and drum should have a number of poles which is
a multiple of all the speed ratios required. Thus 24 by taking successively, 1, 2,
3, 4, 5 and 6 at a time, will give corresponding reductions of 24, 12, 8, 6, 4:8,
and 4 to 1. If, however, no exactly defined ratio is necessary then the number of
magnet poles may be anything suitable, but the armature drum should have a
smooth surface and not be slotted to correspond with the field magnet.
Dated this 1st day of December 1892.
D. STEWART & CO., LTD.,
Duncan Stewart, Director.
WILFRID L. SPENCE,
John Lindsay, Secretary.
COMPLETE SPECIFICATION.
Improvements in or in connection with an Electric Motive
Power System.
We, WILFRID L. SPENCE, Civil Engineer, and D. STEWART & Co., LTD.,
Mechanical Engineers, of The London Road Iron Works, Glasgow, 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 more particularly to an electric rail or tramway system
but it is also applicable, in part, to other purposes where a variable speed reduction
gear is necessary or desirable..
Hitherto shunt wound motors have invariably been found a failure on electric
locomotives. We use shunt wound motors by preference and overcome all objections
to their use by the following means or by some of them.
(1) In the field shunt circuit is placed an automatic switch to cut off the
armature current whenever the exciting current is by any means reduced below a
predetermined minimum. Thus the difference of potential of the supply mains can
never exist across the armature terminals in an unexcited field. This prevents
armature burn-outs due to the momentary interruptions of current which are some-
times caused by bad contact between wheel and rail or collector and main.
(2) Once the automatic switch in (1) has opened the main circuit it can only be
replaced to complete the same when the armature circuit is broken at the driver's
regulating handle. The motions of the two switches being interlocked for this
purpose.
(3) A separate earth connection, by wire brush or otherwise, is provided for the
shunt current, and at the other end this circuit is connected direct to the trolley or
collector and not to the armature terminals. This is to obviate frequent interrup-
tions which might be caused by the automatic switch in (1).
(4) One motor only connected to both axles, is used by preference. This motor
may and should be smaller than either of the two motors on a car of similar size
driven in the usual way by toothed gearing.

page_text: (5) Each wheel axle is driven through an electro-magnetic clutch gear (equiva-
lent to a pall and ratchet wheel) by a connecting rod and crank pin from the motor
spindle.
(6) The motor runs constantly in one direction at a uniform speed independently
of the motion of the car or train. This is rendered possible by,
(7) The variable speed reduction. A system of electric contacts and tripping
gear permits of the clutch in (5) holding only through any desired distance;
during the remainder of the travel, which is constant, it is inoperative by release.
(8) A spring, placed within or alongside of the clutch drum, transforms the jerky
motion of the clutch gear into a uniform one on the wheel axle.
(9) A friction, electro-magnetic, or pall and ratchet brake, which holds only
when the driving clutch is free, prevents the spring in (8) from causing the clutch
drum to run back.
(10) Reversal is obtained by causing the clutch to hold on the return stroke
instead of on the forward one. By this means the energy stored up in the rotating
mass of the armature and in any other masses attached thereto is always available
for facilitating quick reversal of the car in an emergency.
(11) The driver's regulating handle controls only the position of the tripping
gear in (7), ie., the motion of this handle determines only the proportion of the
total stroke of the clutch which shall be effective, it is equivalent to a "cut-off" or
"expansion" gear. It does not affect the main current at all directly, the current
is self-regulating in proportion to the work done. The driver has also the circuit
breaker or switch aforementioned (ep. 2) which may, if desired be operated by
extreme positions of the regulating handle.
nor
(12) No resistances are ordinarily used either in the armature or shunt circuits
is any altering of field connections necessary or desirable.
In quite
exceptional cases both methods may be used as an additional means of speed
regulation.
(13) Alternate current motors, whether synchronising or not, are equally
applicable with direct current machines. This arises from the fact that, under
normal conditions the motor is never stopped, it simply runs free when the car is
being slowed down or is standing.
(14) The exciting current, if necessary with alternate current motors, may be
provided by batteries or through a commutator.
We will now describe the means employed in more detail.
Sections 1, 2 and 3, are sufficiently explicit and do not require further explana-
tion. The interlocking of switches is well understood and in common use in
connection with accumulator plants. The possibility of using a single motor of
comparatively small capacity to drive both axles, (Section 4) will be appreciated
when it is understood that at all times the motor is running at full speed and
consequently at a high rate of efficiency. With the usual arrangement of fixed
ratio gearing the motor must stop when the car stops, and when the current is
turned on for starting, the motor, at the very time when its consumption of current
is greatest, is working at the lowest efficiency. Hence the necessity for two motors,
each capable of developing 15 HP. (if run at full speed) on a car which can be
drawn by two or three horses.
A. form of electro-magnetic clutch gear Figures 1 & 2, is employed on each
axle. It will be seen to consist of an outer casing or field, F, and an inner cylinder
or armature, A. (The function of the parts might equally well be reversed.) The
field carries magnetizing coils, M, and the armature may or may not be similarly
excited. The outer surface of the one and the inner surface of the other should
be notched or slotted so as to present distinct poles. The cylinder is carried by
and drives the wheel axle, W, not rigidly but by means of an elastic connection
the reason for which will be apparent. The outer portion, F, is supported in
bearings so as to be free to turn round the same. A crank pin on the motor shaft
actuates a connecting rod by which a reciprocating motion through an angle of,

page_text: say, 120° is communicated to F. If now the field is excited on the forward and
cut off on the return stroke an intermittent turning motion will be imparted to the
cylinder, A, quite similar in effect to that obtained from pall and ratchet wheel
gear. As the drive is intermittent and jerky the spring aforementioned is desirable
to give smoothness in working; its use however necessitates the employment of a
brake to prevent relaxation or unwinding when the clutch is free or on the return
stroke, it may either be electro-magnetic or mechanical, as for instance a pall and
ratchet wheel.
It will be obvious that by cutting off the exciting current from the field at
different parts of the stroke the clutch will hold through a greater or less angle
and the number of rotations per minute of the cylinder will be varied accordingly.
But it will be equally apparent that the motion is imperfect theoretically for, as
a reference to Figure 4 will show, the stroke of the connecting rod although
variable as to effective length is neverless performed at approximately constant
velocity, hence no variable speed reduction should be possible. However, by the
use of the spring cushion interposed between the magnetic counter-part of the
ratchet wheel and the driven axle the work done, intermittently and at uniform
speed, may be alternately stored up and transmitted so as to produce a practically
uniform turning moment at an angular velocity which shall be about equal to the
mean effective velocity of the electro magnetic pall.
A method of operating the electric contacts by which the variable ratio gear is
controlled is shown by Figure 3. It will be understood that the exciting coils of
the electro-magnetic clutch are included in this circuit although they are not
shown, and further that the illustration is only diagrammatic, for to avoid sparking
at the wiper contacts a double circuit may be necessary, i.e., the clutch coils may.
have to be differentially wound, one set of coils only being in circuit to excite and
both to de-magnetise. And in any case a winding should be adopted which reduces
as far as practicable the "time-constant."
A double series of terminals 1 to 22 are arranged in a circular arc so as to be
traversed by a wiper contact, C, on the motor shaft. Each of these is connected
as shown with a corresponding one on the driver's regulating switch FB. The
current entering at the left passes through the wiper, C, then successively through
the contacts, to 11 or 12 to 22 and on to the regulating switch F B which it
leaves by the segmental plate, D. The action is as follows: In running forward
the handle is turned to F so that D makes contact at first with one, then two, three,
and finally all the connections 1 to 11. Suppose now that the motor shaft is
rotating clockwise as shown and that D is short circuiting the first three plates 1, 2, 3.
As C comes round and touches 1 the field of the clutch is excited and it holds until
the wiper has passed over contact 3 when the circuit is broken. If D is turned as
far as 11 then the circuit remains complete throughout the forward stroke and the
clutch cylinder, A, is rotated through, say, 120 degrees so that the gear effects a
reduction of 3 to 1. This is about the highest possible and it corresponds to
running the car at full speed. To reverse the motion the segmental plate, D, is
turned towards B making contact with terminals 12 to 22. When 12 only is in
circuit the speed reduction may be as low as, say, 24 to 1, 13 gives a higher speed,
14 still higher, and so on until at 22 the reduction is 3 to 1 as before but in the
reverse direction. Figure 4 shows the relative positions of the motor, M, and the
car wheels, W. The numbers 1 to 5 and letters a to e indicate corresponding
positions of the two crank pins on the motor shaft and of the connecting rods and
clutches on the wheel axles.
In order that a single set of contacts, 1 to 22 Figure 3, may serve for controlling
both wheels simultaneously it is better that one connecting rod be below the leading
axle and the other above the trailing one as shewn by the dotted lines Figure 4.
The two crank pins on the driving shaft should be opposite diametrically but as
close together as possible so as to avoid side strains on the motor which may be
hung in any convenient manner either from the car body or on a frame carried on

page_text: A
the wheel axles. Any small relative motion between the driving and driven shafts
due to vibration over a rough road bed has no prejudical effect on the gear.
very convenient construction of the outer portion of the electro-magnetic clutch is
shewn by Figure 1. Each field limb, L, is punched out with a yoke piece, K,
at the back, and the radial depth of the yoke being made equal to the length
of limb all the pieces may be cut out of. straight strips without waste. By having
a large number of poles, say 24, a wider range of speeds may be obtained than
with only 12 as shown, and the arrangement works more smoothly; also in certain
cases it may be desirable to arrange the spacing of the terminals on the regulating
switch board so as to cause the clutch to hold through the angle corresponding to
a definite number of poles as for instance 1, 2, 3, 4, 5, 6, 7 & 8 by which successive
reductions of 24, 12, 8, 6, 4.8, 4, 3-4, and 3 to 1 are obtained. As a rule, however,
no exactly predetermined ratio is necessary and the switch is moved over until the
speed is suitable.
It is possible to work with a smooth surface armature drum, but to increase
the resistance to slipping shortcircuited coils embedded in the core would be
necessary if the transmitted torqué were great, and for this reason the slotted
surface cylinder is preferable as being more efficient. A certain degree of con-
centration of lines in the air space between field and armature is desirable to get
the maximum tractive force, i.e., to make B' as large as possible, With a view to
this each pole piece may be slotted so as to cause the lines to flow in a series of
tufts as shewn in Figure 5, the armature core being slotted to correspond. The
clearance is of course kept as small as possible.
It should be understood that we do not limit ourselves to the use of apparatus
exactly as described; the clutch gear may be of any other suitable form, for
instance instead of being concentric the two portions may be arranged side-by-side
on the axle, and when the clutch is holding they may then be in actual contact ;
the motor shaft may also carry another pair of crank pins at the opposite end, so
placed that their forward or working stroke occurs at the time of the return stroke
of the other pair. By this means the motor is directly performing work during
the whole revolution. The number of contacts, Figure 3, may also be varied, up
or down, but the more the better.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed we declare that what we
claim is :-
1. The combination with the shunt field circuit of an electric motor of an
automatic switch arranged to cut off the armature current whenever the exciting
current falls below a predetermined minimum.
2. In a variable speed reduction gear the combination with an electro-magnetic
clutch of means for causing the same to grip through any variable angular distance
as required, whereby an effect may be obtained similar to that of a ratchet wheel
and pall with variable stroke, substantially as described.
3. The means for making and breaking the circuit of the electro-magnetic clutch
at appropriate intervals which consists of a wiper passing over a series of terminals
connected to a similar series under the control of the driver, substantially as
described and illustrated with reference to Figure 3.
4. The combination with a rotating armature electric motor of a crank pin or
eccentric actuating a connecting rod by which a reciprocating motion is transmitted
to an electro magnetic clutch gear independently controlled to have a variable
period of grip substantially as described.
5. In a variable speed reduction gear the combination with the rotary portion of
an electro magnetic clutch of a spring or elastic cushion through which its turning
moment is transmitted to the shaft so as to give smoothness in working, substantially
as described.
6. The combination with a spring or elastic cushion through which the turning
moment of the electro magnetic clutch is transmitted of an electro magnetic or

page_text: mechanical brake acting during such time as the clutch is free to prevent backward
relaxation or unwinding of the spring, substantially as and for the purposes herein-
before described.
7. Our improvements in an electric motive power system substantially as
illustrated or described.
Dated this 25th day of August 1893.
WILFRID L. SPENCE,
Agent for Applicants.