THE MOTOR
This is a subject so vast and comprehensive, that it will require most
careful thought and attention in order to get a working idea of the
principle. The greatest refinements are resorted to in the building and
handling of engines, and more attention is bestowed on this part of the
automobile than on any other feature for the following reason:
VALUE OF FUEL UTILIZED.--Not more than eighteen per cent. of the value
of the fuel is actually utilized. The rest is waste. A gasoline engine
is a heat motor,--that is, it derives its power from the expansion of
the fuel, and this expansion is produced by the heat.
Now the loss referred to comes about in this way: About 52 per cent. of
the loss is taken up by the water which surrounds the engine cylinders;
from sixteen to seventeen per cent. escapes at the exhaust; and fifteen
per cent. loss is due to conduction and radiation.
THE WASTE.--The great waste, therefore, lies in the cooling means,
which must be employed. The temperature of the ignited gases reaches
fully 2200 degrees, which is over ten times the temperature required to
convert water into steam.
Water absorbs more heat than any other substance, so that this quality
is utilized; but the water, if not kept in motion, when applied to such
a highly-heated surface as an engine cylinder, would be converted into
superheated steam, and would then be of no further value.
WATER ABSORPTION.--This necessitates a constant and intermitting
motion, so that the more rapidly the water moves, the less it will
become heated. At the same time, means must be provided to cool the
water in its circuit back to the engine, and the most efficient means
to accomplish this is to provide a radiator at the forward end of the
machine.
The circulating system, together with the radiator, will be described
under their proper headings.
ENGINE TYPES.--There are two distinct types of engine, one called the
_two-cycle_, and the other the _four-cycle_. _Cycle_ has reference to a
period or turn, in which certain mechanical operations are completed in
regular order so to form a succession of events.
THE FOUR-CYCLE ENGINE.--These events in a four-cycle engine require the
crank to make two complete turns, the order being as follows: Starting
with the explosion of the charge, the first element in the cycle, is
the downward movement of the piston (expansion); second, the return
of the piston to the upper end of the cylinder (exhaust); third, the
downward movement of the piston, on its second revolution, and the
drawing in of a fresh charge of fuel (suction); and fourth, the return
stroke which compresses the fuel for driving the piston down the next
stroke (compression).
THE TWO-CYCLE.--The two-cycle engine, at the explosion, sends the
piston downwardly, and as the crank case and cylinder are connected up
together so as to form an air tight receptacle, within which the crank
and shaft turn, the downward movement of the piston compresses all the
gas which has been previously drawn into the crank case.
When the piston reaches the extreme limit of its downward movement,
it uncovers a port in the side wall of the cylinder, so as to afford
an outlet for the gases of combustion, and immediately thereafter the
piston also uncovers a duct that leads from the crank case, so that
the previously compressed gases, as stated, rush in, and this inward
movement of the fresh gas, also facilitates the movement of the burnt
gases at the opposite side.
COMPRESSION.--When the piston starts on its return stroke, or upward
movement, it compresses the charge thus received, and when the piston
nears the upper end of its stroke the sparking mechanism again explodes
it, so that the cycle is formed by the two operations, performed by a
single turn of the crank shaft.
This latter type of engine is not used to a great extent. It has the
advantage that no valves are used, except the one at the inlet of the
gas to the crank case, and no stems, push rods, cam shafts, or springs
are required to control the movements of the fresh and burnt gases.
Aside from that such engines weigh considerably less than the four
cycle type.
ECONOMY OF FOUR-CYCLE ENGINE.--On the other hand, the four cycle is
more economical, because there is more time for the admission of the
fuel, and for exhausting the gases. Furthermore, it is obvious that in
a two cycle engine more or less of the fresh fuel gas is mixed with and
is discharged from the cylinder with the burnt gases.
As the discharge of the burnt gases and the admission of a fresh
charge, is practically simultaneous, the opening of the discharge is
placed in the cylinder at such a point that the pressure of the gases
cannot be utilized for the full downward stroke, as is the case with
the four cycle type.
[Illustration: THE FOUR-CYCLE ENGINE
Fig. 63. Firing Position.
Fig. 64. Return First Cycle.]
VALVE MOVEMENTS.--Before proceeding to explain the engine in detail,
the different valve movements of a four cycle cylinder are shown, and
this will be of service in explaining the different parts as they are
referred to.
In the construction of engines, as will be more particularly pointed
out hereinafter, the inlet and exhaust valves are usually operated by
mechanical means, but certain engines are so constructed that the inlet
valve is automatic in its operation, and the exhaust valve only is
actuated mechanically.
In the drawings, Figs. 63 to 66, inclusive, both valves are operated
from cams on a secondary shaft, and in the first of these four figures
the crank has just turned the point where the piston is at its highest
limit, and is about to descend. Both valves A B are closed, and the
spark fires the charge, driving down the piston to its lowest limit.
In Fig. 64 the crank is shown about to move the piston upwardly, and
just as it turns the dead center the cam C, on the secondary shaft,
unseats the valve B, through the stem D. As the piston moves upwardly,
the burnt gases are forced out past the valve B.
When the piston reaches the highest point in its first revolution, as
shown in Fig. 65, the stem D drops off the cam C, thus closing the
discharge, and immediately the valve A is opened by the cam E moving
the valve stem F upwardly, and as the piston now descends, fuel is now
drawn in until the piston reaches its lowest point.
In Fig. 66 the crank is turning the dead center, and is about to move
upwardly, and the cams G E are now both in such position that the
valves A B are closed, and when the piston moves up again, to complete
the second revolution, the fuel gas within the cylinder is compressed,
and ready to be fired the moment the crank reaches the position, shown
in Fig. 63.
[Illustration: Fig. 65. Drawing in Charge.]
[Illustration: Fig. 66. Compression.]
THE IGNITION POINT IN THE CYCLE.--In practice, the firing takes place
before the crank has made the turn past the dead center, and this is
called _pre-ignition_, when the spark is advanced too far to the left.
The ignition should take place slightly before the crank turns, because
it takes a small interval of time for the charge to burn the gases,
and during this time the crank will have passed the dead center, and
started on its way downwardly.
From the diagrams it will be observed that two of the strokes, namely
the first and the third, are downward, and the second and fourth are
upward, and that the downward strokes take place during the admission
and impulse, and the compression and exhaust while the piston moves
upwardly.
THE FLY-WHEEL.--As the impulse in this type can take place only at each
second revolution, it is obvious that some means must be provided to
keep the shaft moving during the two turns, and for this purpose the
fly-wheel is utilized.
Practice has found the multi-cylinder type the most valuable, in
connection with the fly-wheel, as in employing two or more cylinders in
line, a smaller fly wheel will be sufficient.
IMPULSES IN 4-CYLINDER ENGINE.--In such a case the four cylinders are
arranged so the impulse will be at four different points of the shaft,
and we may assume that the four cylinders in Figs. 63, 64, 65 and 66,
show the relative positions of the four pistons in a four cylinder
engine.
THE CYLINDER CASE, AND CONNECTIONS.--A cross section of a case and
the relative positions of the various parts, is shown in Fig. 67. The
cylinder A is provided with a water jacket B, so as to form a space C
around the cylinder which has an inlet pipe D at the bottom, and an
outlet pipe E at the upper end.
[Illustration: Fig. 67. Automatic Inlet Valve.]
The inlet valve F is in the head of the cylinder, and it is held
against its seat by a tension spring G. The exhaust valve H is placed
in a lateral extension of the cylinder, in such a position that it is
directly above the secondary shaft I running through the crank case.
The stem J of the valve, is actuated by a cam K on the secondary shaft,
and it is, preferably, made in two parts, the upper being so arranged
that it has a limited longitudinal movement independently of the lower
part, and a spring is arranged so as to provide for longitudinal thrust
in either direction.
The crank shaft M has alongside the crank, a gear wheel N, which meshes
with a gear O on the secondary shaft I, this latter gear being twice
the diameter of the gear N.
PISTON AND CRANK CONSTRUCTION.--The piston is hollow, and the crank
is located as close to the head as possible. This has two or more
circumferential grooves, to receive packing rings. The rings are made
of very hard steel, and are turned up slightly larger than the diameter
of the cylinder, and then cut across diagonally, so they may be sprung
into place, and when in position they will bear against the inside of
the cylinder, and thus serve to prevent the passage of the gases.
CALCULATING THE EFFICIENCY.--The great problem with every beginner is
to know something of the power of the engine, and how it is determined.
Considering that the boy knows nothing of the terms used to designate
the step we shall try to make the following description as free from
technicalities as possible.
In Fig. 68 a cylinder is represented, containing a piston A. B C
indicate the limits of the stroke, and for convenience this space is
provided with eleven marks to represent the pressure of the ignited
gases at various portions of the travel of the piston.
PRESSURE IN EXPLOSION.--When the explosion takes place, at B, the
pressure will be, approximately, 230 pounds per square inch of the
piston. When it moves to the next mark the pressure has decreased to
220 pounds, at the next mark it is 200, and so on, until, at the end of
the stroke, opposite C, the pressure is only 40 pounds.
[Illustration: Fig. 68. Calculating Efficiency.]
EXPANSION LINE.--These figures represent the _expansion_ line. It is
now necessary to get the _mean effective pressure_, which means that we
must know what the average pressure of the gas is in each square inch
from B to C.
MEAN EFFECTIVE PRESSURE.--This is obtained by adding together the
figures given in the sketch, and the result is, 1530. As eleven
pressures were required to produce this sum, it should be divided by
that number, making the result 148, avoiding fractions, as we shall do
in all the calculations.
The figures represent that the mean effective pressure of the gases
on the piston is 148 pounds. If this is multiplied by the area of the
piston, and this result by the stroke in feet and the number of power
strokes per minute, we get what is called _foot pounds_.
FOOT POUNDS.--Assuming that the diameter of the piston is 5 inches,
which, figure, if multiplied by 3.1416, will give its area as a little
over 15-1/2 square inches. Let us assume the crank is 4 inches. This
will give a power stroke of 8 inches.
To find out how many power strokes there are in a minute, we must know
the revolutions, and this being taken at 800, and a power stroke at
only every other revolution, would mean that we have 400 impulses, and
each impulse traveled 8 inches, = 3200.
This represents inches, which must be converted into feet, so that we
have 266 feet of power strokes per minute.
First multiply the mean effective pressure on the cylinder, that is 148
× 15-1/2, which equals 2294. Then, 2294 × 266, equals 610,204. This
product represents _foot pounds_.
WORK OR ENERGY.--A foot pound is the amount of work or energy expended
in raising a weight of one pound, through a distance of one foot. If
550 pounds should be raised one foot in one second of time it would
represent one horse power of work accomplished. If 550 pounds should
be raised one foot in one minute of time it would be equal to 550 × 60
= 33,000 foot pounds, and this would mean one horse power, or the work
done in one minute of time.
[Illustration: Fig. 69. Two-cycle Expansion Position.]
In our above calculation we have determined how many foot pounds we had
in a minute of time, so that if we divide the foot pounds 610,204, by
33,000, we shall get as a result, a little over 18-1/2 horse power.
THE TWO-CYCLE ENGINE.--The longitudinal shell A, Fig. 69, is separate
from the crank case B, the latter being secured to the former by
flanges and bolts, as at C. The piston D is of such length that when it
reaches the limit of its compression stroke, as shown in this figure,
it covers both the supply port E and the discharge port F.
In its outward stroke the upper end clears both of these ports as in
Fig. 71, the discharge port F being the first to open, as shown in Fig.
70.
[Illustration: Fig. 70. Exhausting.]
[Illustration: Fig. 71. Compression.]
CYCLE OF OPERATIONS.--The cycle of operation is as follows: The inward
stroke, which is in the direction of the head of the cylinder, draws
in the gaseous fuel through the valve G, and at its outward stroke the
gas in the crank case B is compressed, and the moment the end of the
piston passes the inlet port E, the gas passes through the duct H into
the cylinder above the piston.
The burnt gases within the cylinder pass out the discharge port F,
facilitated, in a measure, by the compressed inflowing gas. When
the piston again returns, and passes the discharge port, the gas is
trapped, and is compressed during the inward stroke of the piston.
THE CRANK SHAFT.--The most important element in the engine is the crank
shaft. It is usually made of a single steel forging, and out of this
are turned up the crank wrists, the crank arms, and the bearings which
are placed intermediate the different cranks. It is made extremely
large to provide for any strain due to the fuel explosions, and it is
the most difficult part of the engine to turn out.
[Illustration: Fig. 72. Crank Shaft.]
SPECIAL METALS.--Special metals are used by various manufacturers, and
the sizes and structural shapes are now so well understood that few of
them break, although in the early history of the engine this was the
weak and troublesome part of the car.
Improper alining, in the case, and poor or faulty bearings, were
responsible for many accidents, and now means have been found to
overcome most of these objections.
ENGINE TROUBLES.--When we come to consider the engine troubles,
so-called, we shall find there are legions of them. In these days many
of the troubles are easy to remedy, but to remedy them means that the
causes of troubles should be understood. A physician cannot prescribe
for a disease until he has made a diagnosis.
Sometimes the difficulty will be recognized by the symptoms, and is
easily adjusted. But suppose the firing is all right, and the engine
fails to pick up, and seems to be dying out, it may be attributable to
several causes, either one of which would account for it.
DIFFICULTIES POINTED OUT.--If the engine seems to run down, and fails
to pick up quickly, it may be due to water in the carbureter, or to a
weak battery, or to leaks in the water jacket that will admit water
into the compression chamber, or the trouble may be faulty compression.
Other things should be looked up: The pump may be out of order, the
connections loose, and thus permit waste through the leaks, or there
may be a stoppage somewhere in the water circulation, or the water
may be exhausted, or the gasoline too low or too poor for the kind of
carbureter which you have.
If anything is due to the engine itself, in the vast majority of cases,
it is due to poor compression. The engine is too often blamed for
faults which belong elsewhere. Nevertheless, it is well carefully to
examine the bearings, to look over the clutch, and the bearings in the
line leading to the drive shaft.
STARTING THE ENGINE.--In starting, some engines give a great deal
of trouble, usually due to wrong adjustment of the sparking device.
This should not be advanced too much. If the trouble is not at that
point, it may arise from too weak a suction, or an obstruction in the
carbureter itself.
CARBURETER.--At slow turning speed of the engine, the carbureter is
very sluggish, because it must be started up from a condition of
repose, and unless there is the best of compression, the suction will
not be sufficient to dislodge or move the slightest impediment which
may be in the way.
LOW COMPRESSION.--Low compression arises from numerous causes. A
carelessly screwed sparking plug; defective or partly blown out
gasket in the cylinder head; loose, or partly open compression cock;
a sticking valve; a rusted, or defective inlet valve; leak in the
combustion chamber; or a worn or scratched cylinder.
Whenever it is possible, the engine should be examined to observe the
condition of the piston rings. Sometimes the rings will break into
small pieces, and these parts will wear the most perceptible creases in
the cylinder walls. When such is the case they will have to be taken
out and lapped.
MIXTURES.--Too rich a mixture has the effect, in many cases, of causing
a deposit of carbon which is bad for the engine. It coats the walls of
the cylinders, and is hard to remove. The application of petroleum and
alcohol, if allowed to remain in the cylinder for some hours, will aid
in taking it out, but removing the cylinder and scraping is the only
safe method.
The usual way to test the cylinders to see whether either misses fire,
is to cut out all of the spark plugs except one, and then test that,
and so with all the others in succession, and in this way the location
of the trouble will be discovered.
SPARK PLUGS.--It is also the case that carbon deposits on the plug
points will become heated up to such a point that pre-ignition will
take place. Over-heated cylinders may cause this, and in certain cases,
where the rotor arm wears, at the contact point, it leaves a trail of
metallic particles over which the current will travel.
THE WEATHER.--Cold weather is often a serious check to the starting of
an engine, the water jacket, or some of the piping may be frozen, or
the lubricating oil may become too thick to render proper service.
DRAINAGE.--A careful operator will see to it that when the car is left
all the water will be drained from the pipes and the water jacket and
pump, and the parts can be dried out by running the engine for a minute
or so, during the time of draining, so as to heat up the parts.