breaker and the blow-out coil in the controller being depended upon to
prevent the lightning charge from passing.
=Lamp Circuits.= The lamp circuit of a car is protected by its separate
fuse box, and usually each lamp circuit has a switch. As explained
before, five 100-volt or 110-volt lamps are placed in series between
the trolley wire side of the circuit and ground. If one lamp in the
series burns out, of course, all five are extinguished until the
defective lamp is replaced with a new one. Enclosed arc lamps are
sometimes used for car lighting.
Cars to be operated from either end are often wired so that by turning
a switch the platform light on the front end, a light for the sign
and another for the headlight on the rear end will be extinguished
and corresponding lights on the rear and front ends lighted. This is
accomplished by the method of wiring shown in Fig. 37. The interior
of the car is lighted by six lights. Headlights of 32 candle power
are used. This method requires the use of two switches. In all light
wiring schemes a switch should be placed on the trolley side of the
lights. This permits the current to be cut off in the event of a ground
occurring in the system.
On interurban cars arc headlights are almost invariably used. The
circuit for the headlight after passing through a switch in the
motorman’s cab goes through a resistance frame usually underneath the
car and terminates in a socket near the car bumper. The brackets on
which the lamp is hung are grounded so that whenever the plug from the
lamp is inserted in the socket and the switch in the cab is turned on,
the circuit is made.
Usually there is a pressure of about 60 to 70 volts at the terminals
of the lamp. The remainder of the voltage drop, from 500 or 600 volts
(or whatever the line may be), is in the resistance under the car.
The current through the lamp is usually about four amperes. With 60
volts at the arc and 500 volts on the line, this gives a consumption
in the lamp of 240 watts and a loss in the resistance under the car of
2,000 watts, or about 90 per cent. The use of the headlight resistance
to cut the voltage down is therefore a very inefficient method. Some
schemes of wiring use the incandescent lamps used in lighting the car
as resistance for the headlight. Another way is to light the interior
of the car with arc lamps placed in series with the arc headlight.
=Trolley Base.= The trolley base upon which the trolley pole
swivels, and which furnishes the tension that holds the trolley wheel
against the wire, is designed to maintain, by means of springs, an
approximately even tension against the trolley wire, whether the
trolley wire is high above the track or near the car roof. This is done
by changing the relative leverage which the springs of the trolley base
have on the trolley pole according to the height of the trolley pole.
[Illustration: Fig. 38. Trolley Base.]
[Illustration: Fig. 39. Trolley Wheel.]
Fig. 38 shows one form of trolley base. The trolley base is bolted to
a platform constructed for it on the roof of the car; and the supply
wire to the motors and other electrical devices on the car, except in
cases where a wooden trolley pole is used for certain special reasons,
is connected directly to the trolley base. An insulated trolley wire is
run down the wooden trolley pole, and connected through a flexible lead
to the car wiring.
=Trolley Poles.= The trolley poles in general use are of tubular steel,
which gives the greatest strength for a given weight, and which can
usually be straightened if the pole has been bent by striking overhead
work when the trolley wheel leaves the wire.
=Trolley Wheels.= Trolley wheels are from four to six inches in
diameter over all, the small wheels being used in the city service, and
the large wheels in high speed interurban service. A typical trolley
wheel is shown in Fig. 39. Various companies use various forms of
groove in the trolley wheels, some adopting a groove approximately
V-shaped. The U-shaped groove, however, is the most common. The trolley
wheel is made of a brass composition selected for its toughness and
wearing qualities.
[Illustration: Fig. 40. Trolley Harp.]
=Trolley Harp.= The trolley harp, which is placed on the end of the
trolley pole and in which the trolley wheel revolves, usually has some
means for making electrical contact with the wheel in addition to the
journal bearing. In the harp illustrated in Fig. 40, which is a typical
form, this additional contact is secured by a spring bearing against
the side of the hub of the wheel.
[Illustration: Fig. 41. Third Rail Shoe.]
Since trolley wheels revolve at a very high speed, some unusual means
of lubrication must be provided, since there is no opportunity for
ordinary oil or grease lubrication. Graphite, in the shape of what is
called a “graphite bushing,” is most commonly used. This is a brass
bushing, which is pressed into the hub of the trolley wheel. In this
bushing is a spiral groove filled with graphite which is supposed to
furnish sufficient lubrication as the bushing wears. Roller-bearing
trolley wheels have been used to a limited extent, with considerable
success in some cases. Some companies have done away with the graphite
bushing, and have provided a very long journal for the trolley wheel
instead of the usual short bushing.
=Contact Shoes.= The contact shoe most commonly used on roads employing
the third rail is shown in Fig. 41. This is simply a shoe of cast iron
hung loosely by links. The weight of the shoe is sufficient to give
contact. The motion of the links permits the shoe to accommodate itself
to unusual obstructions and variations in the height of the third rail.
The shoe is fastened to the truck frame by means of a wooden plank
which furnishes the necessary insulation.
[Illustration: Fig. 42. Sleet Wheel.]
The Potter third-rail shoe which has been used to a limited extent,
employs a spring for giving the necessary tension to make electrical
contact between the shoe and the third rail. In some ways this is
superior, because a spring tension is quicker in its action than
gravity, and the shoe accommodates itself better to variations in the
height of the third rail at very high speed. The wear on the shoe,
however, is likely to be greater.
=Sleet on Trolleys and Third Rails.= The deposit of sleet on trolleys
and third rails hinders greatly the operation of cars. Often sleet
wheels of the type shown in Fig. 42 are used as a trolley wheel. These
cut the sleet off instead of rolling over it.
On the third rail, scrapers and brushes in advance of the contact shoe
are usually effective where trains are frequent. Several roads are now
melting the sleet on the rails by the use of a solution of calcium
chloride. The solution is stored in a tank on the car and is led
through small pipes to the rail immediately in front of the collecting
shoe. About one gallon of solution is used per mile, making the cost
about 7½ cents per mile. The effects of one treatment last for two or
three hours during the continuance of a storm.
Solutions of common salt have been used in the same manner, but it is
claimed that the corroding action on the iron of the calcium chloride
is not as great as that of a salt solution.
TRUCKS.
Electric railway cars are classified generally as _double-truck_ and
_single-truck_ cars. Double-truck cars are those that have a truck
that swivels at each end of the car. A single-truck car is one having
four wheels.
[Illustration: Fig. 43. Brill 21-E Car Truck.]
=Single Trucks.= A great many types of single trucks have been
designed. It would be out of the question to discuss them all here. In
general, however, it may be said that truck builders have aimed to make
a truck frame in itself a complete unit independently of the car body,
so that the car body will simply rest upon the trucks and there will be
no strain on the car body in maintaining the alignment of the truck.
Most single trucks, therefore, consist of a rectangular steel frame,
either cast or forged, riveted or bolted together. This frame holds the
journal boxes in rigid alignment. Usually a spring is placed between
each journal box and the truck frame. This spring may be either spiral
or elliptic. The principal springs, however, are between the truck
frame and the car body. Most truck builders have used a combination
of spiral and elliptic springs between the car body and truck frame,
as this combination is considered to give better riding qualities
and greater freedom from teetering or galloping than either spiral
or elliptic springs alone. Fig. 43 shows a Brill single truck, which
illustrates all of the features enumerated.
=Swivel Trucks.= Swivel trucks, commonly called _double trucks_, are
made in many forms, but the most common is that known as the M. C.
B. type of truck. This truck is similar to the standard truck which
is in universal use on steam railroad passenger cars in the United
States. Different truck builders have introduced many variations in
this general type of truck, in adapting it to electric service. Some
modifications from the steam railroad standard truck were necessary to
accommodate the electric motors and to permit in some cases a low-hung
car body. Such trucks are made in a great variety of sizes.
[Illustration: Fig. 44. St. Louis Car Company Truck.]
Fig. 44 shows one of these trucks built by the St. Louis Car Company.
In this type of truck the car body is fastened to the truck only by
the kingbolt on which the truck swivels. This kingbolt is placed in
the center of the truck bolster. There are also side bearings between
the car body and the ends of the bolster, to prevent tipping of the
car body when it is unbalanced. The arrangement of this part of the
truck is shown in Fig. 45. Under this bolster are elliptic springs
which rest on what is called the _spring plank_. This spring plank
is hung from the rectangular frame of the truck by links which allow
a side motion. This side motion gives easier riding, especially upon
entering and leaving curves. All trucks having this feature are known
as _swing bolster trucks_. The weight, being transmitted to the transom
and truck frame through the swinging links just referred to, is then
taken by the equalizer springs that support the rectangular truck frame
on equalizing bars, which equalizing bars rest on the journal box at
either end and are bent down to accommodate the springs located between
them and the truck frame. The truck frame holds the journal boxes in
alignment by means of guides which permit an up-and-down movement
without movement in any other direction, just as on all other types
of truck. It is thus seen that there are two sets of springs between
the car body and car journals; one set of spiral springs between the
equalizing bar and truck frame; and one set of elliptic springs between
the spring plank and the bolster. All shocks must be transmitted first
through the spiral springs and then through the elliptic springs. The
motors used on this type of truck usually have nose suspension, the
nose of the motor resting either on the bolster of the truck or on the
truck frame.
[Illustration: Fig. 45. Bolster, Links and Spring Plank.]
[Illustration: Fig. 46. Steel Tire Wheel.]
There are a number of swivel trucks made which have departed
considerably from M. C. B. lines, but nearly all retain the features
of a bolster mounted by springs on a spring plank, a spring plank hung
from a transom, a transom rigidly fastened to the rectangular truck
frame of which it forms a part; and a truck frame with one or more sets
of spiral springs between it and the journal boxes. =Maximum Traction
Trucks.= A type of swivel truck that once was very popular but has
largely been superseded by the type just described is the “maximum
traction truck.” This truck has two large wheels on an axle which
carries 60 to 70 per cent of the weight on the truck, and two small
wheels carrying the balance of the weight. The motors are on the large
wheels.
=Car Wheels.= The car wheels most commonly used are of cast iron.
In order to make a tread and flange upon which the wear comes, hard
enough to give a good mileage, the tread and flange are chilled in the
process of casting. Around the periphery of the mould in which the
wheels are cast, is a ring of iron instead of the usual sand. When
the molten cast iron comes in contact with this ring of iron, which
is called a “_chill_,” the iron is cooled so suddenly that it becomes
extremely hard. The balance of the wheel, cooling more slowly since it
is surrounded by sand, has the hardness of ordinary cast iron. A steel
tire wheel is shown in Fig. 46.
[Illustration: Fig. 47. Elevated Car Axle.]
Wheels with steel tires are coming into use for elevated and interurban
cars because their flanges are not so brittle as those of cast-iron
wheels. In wheels of cast metal there is always a liability that
the flanges and tread will chip and crack. On high-speed cars the
falling-out of pieces of flange may be a serious matter and result in
a wreck. Steel-tired wheels have a hub and spokes either of cast or
forged steel or iron. On to this wheel a steel tire is shrunk. The
tire is heated in a furnace built for the purpose, and is then slipped
over the wheel. It is made just such a size that it will slip over the
wheel when hot, and when it is cool it will shrink enough to make a
very tight fit. When the tire is to be removed after it is worn out, it
is heated until it has expanded sufficiently to drop off.
An axle for elevated car is shown in Fig. 47.
When cast-iron wheels are worn to an improper shape or have flat spots
upon them, due to the sliding of the wheels with the brakes set, an
emery wheel grinder must be used to grind them down, as nothing else is
hard enough to have any effect on the iron.
[Illustration: Fig. 48. Standard M. C. B. Flange.]
When steel-tired wheels are worn, they can be put in a lathe and the
surface of the tire turned off, as this surface is of metal soft enough
to be workable with ordinary tools.
[Illustration: Fig. 49. Brake Shoes and Levers.]
The types of wheel tread and wheel flange in use vary greatly among
different electric railways. There is a standard Master Car Builders’
wheel tread used on steam railroads, which is shown in Fig. 48.
Electric railways, however, are usually obliged to use a smaller flange
and narrower tread. Street railway special work, such as switches and
crossings, usually has too shallow a flange way to permit a standard
M. C. B. flange to pass through. Some street railways use flanges as
shallow as ⅜-inch, although ¾-inch is most common on city work. The
width of the tread on street railway cars, that is, the width of the
wheel where it bears on the rail, is usually from 1¾ inches to 2¼
inches. There is a tendency, however, on electric railways, on account
of the increasing number of interurban cars which must use city tracks,
to build tracks that will accommodate wheels approaching the M. C. B.
standard of steam roads. A few roads have adopted wheel treads and
flanges very near to the M. C. B. standard.
[Illustration: AUTOMATIC AIR BRAKE CAB EQUIPMENT.
Westinghouse Air Brake Co.]
=Brake Rigging.= The brake rigging on a single-truck car may be
arranged in a variety of ways, but should be such that a nearly equal
pressure will be brought to bear on the brake shoes on all four wheels.
A typical arrangement of brake shoes and levers for single-truck cars
is shown in Fig. 49. The rods R terminate in chains winding around the
brake staff upon which the motorman’s handle or hand wheel is mounted.
[Illustration: Fig. 50. Brake Levers and Air Brake.]
For double-truck cars the brake rigging is necessarily more
complicated, as it must be arranged to give an equal pressure on all
eight wheels of the car. Brake shoes are sometimes placed between the
wheels of a truck and sometimes outside. The arrangement of brake shoes
between wheels is apparently finding most favor, as when the shoes are
applied in this position there is less tendency to tilt the truck frame
when the brakes are applied, and this adds to the comfort of passengers
in riding. Fig. 50 shows one form of arrangement of brake levers common
on a double-truck car equipped with air brakes, with inside-hung brake
shoes.
=Brake Leverages and Shoe Pressure.= The levers between the air
cylinder and the brake shoes are usually so proportioned that with an
air pressure of 70 lbs. per sq. in. in the brake cylinders the total of
the brake shoe pressures on the wheels will be equal to about 90 per
cent of the weight of the car. The diagram Fig. 51 has shoe pressures
and strains in the several rods marked on shoes and rods.
The following example, based on the diagram, will explain the lever
proportioning. Only round numbers are given on the diagram.
Assume a four-motor car weighing 40,000 pounds. A brake cylinder 7
inches in diameter is used. This gives 38.5 square inches and at 70
pounds air pressure a total force on the piston rod of 2,695 pounds.
The weight of the car is 40,000 pounds. Taking 90 per cent of this
gives a total of 36,000 pounds to be exerted by the brake shoe when an
emergency stop is made. Each of the eight shoes will press against the
wheels with a force of 4,500 pounds.
The dimensions of the truck are such that the “dead levers,” those
fixed at one end and which carry shoes, cannot be over 13 inches long.
The shoe will be hung three inches from one end, making the proportions
10 to 3, and the pressure on the strut rod between shoes will be 4,500
× ¹⁰⁄₁₃ or 3,461 pounds. To clear the truck frame the live lever
extends 14 inches above the point of application of the brake shoe.
To obtain 4,500 pounds pressure on the shoe, the distance between the
brake shoe and the strut rod, which we will call “_x_,” will be found
by regarding the upper end of the lever as fixed and the power applied
at the lower end.
14 + _x_
4500 = 3461 × ———————— or
14
_x_ = 4.2 inches.
Now to obtain the force required in the rod to the truck quadrant,
the bottom end of the live lever must be regarded as the fulcrum. The
equation is
4.2
_x_ = 4500 × ———— = 1038 pounds.
18.2
As the pull rods from each side of the truck are attached to the truck
quadrant, the stresses in the brake rods are double this, or 2,076
pounds.
[Illustration: Fig. 51. Diagram of Brake Shoe Pressures and Strains.]
The position of the brake cylinder under the car restricts the length
of the “live” and “dead” cylinder levers to 16 inches. To obtain 2,076
pounds pull on one end of the levers with the previously computed 2,695
2076 _x_
pounds on the other, the proportions must be ———— = ———, since 2076 +
4771 16
2695 = 4771. Then _x_ = 7 inches, the distance from the brake piston to
the pivotal point.
Since 2,695 pounds pressure is exerted and 36,000 pounds results the
proportion of the whole system of levers is 36,000 to 2,695 or 13.3
to 1. In other words the travel of the piston in the cylinder will
be 13.3 times that of the shoes if there were no lost motion to be
taken up. The piston travel should be from 4 to 5½ inches. This gives
about ⅜-inch travel of the brake shoes. Increased travel of the brake
shoes necessary to set them as they wear away causes increased travel
of the piston of the air cylinder. Not only is more air used at each
application of the brakes but the brakes are slower in acting. It is
therefore necessary to adjust the brakes frequently. This is done
in the system shown in the diagram by the use of a turnbuckle in the
connecting rod between the live and dead levers of the truck.
When two motors are on one truck and none on the other, allowance must
be made in the levers for the increased weight of the motor truck and
the inertia of the armature. The leverage on the motor truck must be
greater than on the other.
=Air Brakes.= Air brakes used on electric railway cars are usually of
what is called the _straight air brake_ type in distinction to the
_Westinghouse automatic air brake_. A straight air brake is one in
which the air is stored in a reservoir; and, when the brakes are to
be applied, air from this reservoir is turned directly into the brake
cylinder, in which works a piston operating the brake levers. Air
admitted behind the piston forces it out with a pressure which applies
the brakes. When the air is let out of the brake cylinder, a spiral
spring forces the piston back to its original position and the brakes
are released. The motorman’s valve by which he applies the brakes,
therefore, provides, first, for turning air from the storage reservoir
to the brake cylinder to apply the brakes, and, second, for closing the
opening to the storage reservoir and opening an exhaust passage from
the brake cylinder so that the air can escape from the brake cylinder
to release the brakes.
Straight air brakes of this kind would not be suited to the operation
of long trains, because, if the air-brake hose connection between
cars should be broken, the brakes would be useless; but for trains of
one or two cars, such as are common in electric railway practice, the
simplicity of the straight air brake outweighs its disadvantages and
this is the type of brake usually employed. (See Fig. 52.)
The Westinghouse and other forms of automatic air brake are used on
electric railways where cars are operated in long trains; but it is out
of the province of this paper to describe these brake systems fully, as
they are rather complicated. It may be said in general, however, that
the Westinghouse automatic air brake is so arranged that, should the
hose connection between cars be broken, should the train pull in two,
or should anything happen to reduce the pressure which is maintained
in the train pipe that runs the length of the train, the brakes would
immediately be applied on the entire train. [Illustration: Fig. 52.
Diagram of Straight Air Equipment.]
=Compressors.= A small air compressor driven by an electric motor is
frequently employed on electric cars to keep the storage reservoir of
the car supplied with air. These air compressors are carried under
the car or in the motorman’s cab. They are generally arranged with an
automatic device which closes the motor circuit and starts the motor as
soon as the air pressure falls below a certain amount; and the motor
will continue in operation pumping air until the pressure rises to the
amount for which the automatic device is set. The pressure carried in
the storage reservoir is usually from 60 to 90 pounds per square inch,
which, as a general thing, is considerably more than is required to
apply the brakes hard enough to slide the wheels.
=Automatic Governor for Air Compressors.= Automatic governors are often
installed in connection with air compressors in order that a fairly
even air pressure may be maintained in the storage reservoir. In these
the fall and rise of the air pressure within certain limits closes and
opens the circuits to the motor. In some styles the air acting on a
piston operates the circuit breaker.
The diagram shown in Fig. 53 shows the principle of the Christensen
governor, in which the air pressure is employed to make and break a
secondary circuit.
When the pressure in the storage reservoir falls below a predetermined
value, the hand of the air gauge makes contact with lug A. This closes
the circuit through solenoid No. 1. Lug D, mechanically connected to
the armature of the solenoids is pulled in contact with lug C, and this
closes the circuit to the motor, and shunts the winding of solenoid No.
1. When the air pressure rises to a predetermined value the hand of the
air gauge is thrown in contact with lug B. This energizes solenoid 2
by connecting it across the motor terminals. The armature is pulled to
the right and the circuit to the motor is broken. When this is done it
is evident that the current through the energized solenoid is broken.
It is evident from the description that current passes through the
solenoids only during the short periods that the armature is moving
from one position to the other and the air gauge never has to break a
circuit in which there is an appreciable voltage so that there is no
arcing at lugs A and B.
[Illustration: Fig. 53.]
A blow-out coil in series with the motor is provided immediately under
lug C which extinguishes the arc at that point when the motor circuit
is broken.
A Westinghouse air compressor is shown in Fig. 54.