TRANSMISSIONS, TYPES, OPERATION AND CARE
Transmission came into use with the application or adoption of the
internal combustion engine as a factor in motor car propulsion.
As this type of engine develops its power by a rapid succession of
explosions in the combustion chambers, each explosion delivers an
impulse or power stroke to the piston, which in turn sets the crank
shaft and flywheel to revolving. The momentum gathered by the crank
shaft and flywheel may therefore be termed the power for duty, or in
other words, unless there is momentum or carrying motion at this point,
there will be little or no power for duty.
This brings us up to a point where it is easy to see that a rapid
series of explosions are necessary to gain carrying momentum or power
to move a dead weight load. As this motional power could not be applied
to the load without serious damage to the gears and bearings, it
was necessary to invent a device to gradually transmit or apply the
power to the movable load by graduating the leverage. This resulted
in the development of the automobile transmission. The natural way of
doing this at first seemed to be by applying the power to the load by
frictional slippage. Many ingenious devices of this sort were tried out
without much success until the driving and driven disc type made its
appearance.
Fig. 109 shows the driving and driven disc type of friction
transmission. This type of transmission is not being used by any of the
present day manufacturers of automobiles, but may still be found on
some of the three and four-year-old models still in operation.
A, the drive shaft, is squared and slides backward a distance of three
inches through a squared sleeve extending from the hub of the flywheel.
The action of this shaft is controlled by a leverage arrangement to a
foot pedal. B, the steel plate driving disc, is attached to the end of
shaft A, and drives C, when held back against it by pressure on the
foot pedal. Disc C can be slid in any position on the jack or cross
shaft D, and is controlled by a leverage arrangement connected to a
hand lever. The various speeds are obtained by sliding disc C into
different positions and contacts on the left side of disc B. Reverse
speeds are obtained by sliding disc C over center where it forms
contact on the right side of B and is driven in an opposite direction.
[Illustration: Fig. 109. Friction Transmission]
=The Planetary Type of Transmission.=--The planetary type of
transmission made its appearance along about the same time as the
friction type. The power is transmitted to the load through a set of
reduction gears arranged in a drum. A king gear on the engine shaft
operates a set of small gears in the drum. These small gears reduce
the leverage speed and transmit the power to the drive shaft, a band
similar to that used on brakes is fitted to the face of the drum. When
this drum containing the reduction gears is not in use it turns at
crank shaft speed. The speed is used by pressing a foot pedal which
tightens the brake band and holds the drum stationary, thereby forcing
the smaller gears into action.
Planetary transmissions are shown and fully explained in a later
chapter. (See Model T Ford Supplement.)
=The Sliding Gear Transmission.=--This type of transmission has
proved very successful, and is used by 98 per cent of the present day
automobile manufacturers. This type of transmission made its first
appearance with a progressive gear shift, that is, it was necessary
to proceed through one speed or set of gears to engage the next. This
arrangement caused considerable confusion at times, as it was necessary
to reshift the gears back through these speeds to attain neutral, when
the car was brought to a stand still.
[Illustration:
Neutral
2nd.
Rev.
Rev.
2nd.
Neut.
1st.
3rd.
3rd.
1st.
Ball-and-Socket
Shift
H or Gate Type
Gear Shift
Fig. 110. Selective Type of Gear Shifts]
[Illustration: Fig. 111. Sliding Gear Transmission--Sectional View]
The control lever operated on a straight forward and backward direction
on a quadrant, having a notch for each speed change. This gear shifting
arrangement has also been abandoned by manufacturers in favor of the
selective gear shift which is arranged so that the driver may choose
any speed at will. Fig. 110 shows the control lever which operates in a
frame resembling the block letter H and the ball and socket shift which
operates in the same manner. Fig. 111 shows the complete assembly of
the selective sliding gear transmission. The sliding gears are arranged
on a separate core and are operated by an individual throw fork, which
seats in a groove on the shoulder of the gear. Low and reverse are
always opposite each other on the same core. High and intermediate are
located on another core, and are controlled by another individual
shifting fork. The gear box arrangement (Fig. A) shows the cast gear
box which contains the gears, shafts, and bearings, and a roomy
compartment below the gears in which grease is carried, as the gears in
this type of transmission always operate in an oil bath which prevents
excessive wear and causes them to operate noiselessly. Fig. B, the gear
case cover, contains the slotted sliding shafts, to which the gear
in shifting forks are attached. Fig. C shows the arrangement of the
gears in the case and explains their operation. Gear No. 1 is attached
to the extreme end of the engine shaft, and is continually engaged
with gear No. 4, which causes the counter shaft No. 11, containing
the stationery gears, to revolve whenever the engine shaft No. 9 is
in operation. The drive shaft No. 8 does not run straight through and
connect with No. 9, the engine shaft, but ends and takes its bearing in
the core of gear No. 1. Consequently, when the gears on the drive shaft
are slid into mesh with the gears on the counter shaft, variable speeds
are attained. Low speed is obtained by sliding gear No. 3 into mesh
with gear No. 6; second or intermediate is obtained by meshing gears
No. 2 and gear No. 5.
High, or engine speed, is obtained by sliding gear No. 2 which is cored
and shouldered over the end of gear No. 1, making a direct connection
of the drive shaft No. 8, and the engine shaft No. 9, at this point.
Reverse is obtained by meshing gear No. 3 on the drive shaft with gear
No. 10, which is an extra or idle gear mounted on a stub shaft on the
rear of the gear case. Idle gear No. 10 is always in mesh with gear No.
7, on the counter shaft.
Functional operation engine shafts always turn to the right or
clockwise, which causes the counter shaft to turn to the left or
anti-clockwise. This causes the drive shaft to turn to the right when
low or intermediate speed gears are engaged, driving the car forward.
Reverse, is obtained by the use of an extra gear in this way. Counter
shaft turning to the left turns idle gear to the right, and this gear
turning to the right, turns gear on the drive shaft to the left, and
causes the car to be driven in a backward direction. In the unit power
plant shown in Fig. 112, the operation and gear shifting are identical
with that of the separate gear case. The crank case of the motor is
either extended or another case attached to the motor which has a
compartment arranged to contain the clutch and transmission gears. This
arrangement results in compactness, and does away with the supports
required to carry the transmission separately.
=Transmission Care.=--The transmission should be thoroughly cleaned and
refilled with fresh grease or heavy oil once in every thousand miles
that the car is driven to prevent excessive wear and much noise. To
clean, remove the plug at the bottom of the case, and the cover from
the top. After the old oil has drained out, replace the plug, fill
the case half full of kerosene, replace the cover, and let the motor
run for a few minutes with the gears in neutral. Drain the kerosene
off, and wash the case and gears off with a paint brush which has been
dipped into fresh kerosene. Then examine the gears for blunt burrs
and the bearings for looseness. If the gears are burred or chipped,
file, or grind them down to level. If the bearings are loose they will
have to be replaced, as the bearings used to carry both the counter
and drive shaft are seldom provided with means of adjusting. These
bearings, however, will not show wear for years if properly cared for.
Next, see that the gear case is free from grit and filings, replace the
drain plug, and fill the gear case to within one half inch from the
drive or propeller shaft with a light graphite grease or heavy oil, and
replace the cover using a new gasket.
[Illustration: Fig. 112. Clutch and Transmission Assembly--Unit Power
Plant]