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DEVELOPMENT OF TRANSMISSION

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MSU Is An Affirmative Action/Equal Opportunity

DEVELOPDENT OF TRANSI-IISSION

BY

MUNIAPPA PAPIAH

w

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Mechanical Engineering

1949

1'HESlS

 

 

ACKN WEE DGI-EN T

It is a very great pleasure to acknowledge my
indebtedness to Professor G. W, Hobbs, in charge of
Automotive Engineering. From the beginning to the end he
was kind enough to guide me. Without his encouragement,
his constant and sympathetic aid, this paper would have
been impossible.

I am also grateful to the Government of India for
selecting me for higher studies in the U.S.A. and to

Michigan State College for all their kindness and courtesy.

ABSTRACT

An internal combustion engine does not develOp
its full power at low speeds; therefore, an automobile can-
not pull much of a load at low speed, and gears must be in-
terposed between the engine and driving wheels. This per-
mits the crankshaft to turn at a Speed necessary to produce
the desired power while the wheels turn at a speed required
by road conditions or grades. To secure flexibility of
Operation 3 and sometimes 4, speed ratios are provided. To
back the car, a set of gears are arranged in the transmis-
sion. The gears, shafts, and other parts necessary for
varying the forward speed and obtaining a reverse are all
contained in a housing or gear box, and the assembly is
called a Transmission or a Torque Converter.

The transmission may be located:

(a) as part of a unit with the engine and clutch

(b) as a separate unit between the clutch and

rear axle

The main purpose of a transmission, therefore, is
to provide suitable gear ratios between the engine and rear
wheels for all driving conditions and to give a greater out-
put torque than the engine torque. The torque ratios can be
secured in several ways.

Types of transmission:

1. Sliding gear transmission

2. Hydraulic torque converter

3. Hydraulic drive

Old style progresggye type. This type was dis-
carded'because it was necessary to pass one gear through
another, which made a clashing noise and was difficult to
Operate at times.

Selective gear type transmission. This is so
called because_it_is possible to engage any set of gears
desired in moving from the neutral position without passing
through any other gears. This type is preferable because
of the absence of noise from the gears and the ease of oper-
ation. we have to remember that gears cannot be shifted
until the lever is brought to neutral position.

Some modern transmissions now use either hydramatic
drive or dyna flow. The combination of a fluid coupling and
a fully automatictransmission is an ideal unit for transmit-
ting power from the engine to the wheels. This drive takes
the place of two conventional units, the clutch and the

selective sliding gear transmission.

TRANSMISSION

Internal gears run more silently than spur
gears: -

American motorists want their cars tO have excep—
tional performance. They want them to be capable of great
acceleration without the inconvenience of frequent gear
shifting. To meet their demands, manufacturers have in-
creased their engine speeds and at the same time increased
the rear axle ratios. In this way, they found it possible
to increase both the acceleration on high and the limiting
grade which can be climbed on high gear, without increasing
the engine weight.

Up to 35 mph. the engine power reserve is almost
as large with the smaller as with the larger rear axle
ratio. The main advantage gained by decreasing the rear
axle ratio is that the average engine speed is much lower,
in consequence of which the Operation is much smoother and
the wear and tear Of the engine is reduced.

Recourse was, therefore, had to the internal gear
which is both more efficient and more quiet than the spur
wheels. There is no power loss when one perfectly elastic
solid rolls over another, and hardened steel has a high
degree of elasticity.

This transmission uses internal gears instead of

dogs. The gear has internal teeth which mesh with a smaller

2
gear on the inside of gear. The gear shift lever is usually
_ of the ball and socket type. The movement of lever is in a

ball and socket.

_ 3 Speed and 4 Speed Transmissions

One of the most important of these relates to the
number of changes Of gears. This is a somewhat involved prob-
lem, as it affects the type and size of engine to be employed,
the rear axle gear ratio, the design of other units such as
the clutch, prOpeller shaft, universal joints, the weight of
the car, and its stability.

Easier shifting and quicker Operation in next-tO-top
speed appears to have been attained by the use of the 4 speed
transmission. Quiet Operation and easy shifting can be and
are realized in some 3 gear sets also.

Advantages of 4 speed gear sets:

1. Fewer engine revolutions per mile with result-
ing decrease in engine wear and friction losses.

2. Lower engine speeds with consequent decrease in
engine noise and vibration, and less fatigue in driving.

3. Lower propeller shaft speeds resulting in less
whip and noise, or permitting the use of lighter and less ex—
pensive parts.

4. Improved fuel economy resulting from a better
load factor, and lower oil consumption.

5. Ability to accelerate more rapidly without ex-

cessive gear noise in the next-to-top speed.

3

6. Shorter steps between gears, and a lower gear
for emergency use.

7. General excellent performance in third speed in
traffic.

Whatever the design may be, we have to retain the
standard shift in any new gear set that may be adOpted. If
we are to have 4 speeds, the 3 top Speeds should require the
same shifting as the 3 speed type, the emergency low speed
being latched out or otherWise arranged to prevent accidental
engagement. Any other arrangement is likely to confuse Opera-
tors in emergencies and lead to many accidents otherwise

avoidable.

Internal Gears:

In a 4 speed transmission, changes from 3rd to 4th
speed and vice versa will be more frequent than any changes
Of gears in a car with a 3 speed transmission, and so it is
essential that the gear be so designed that this change can
be made easily. It is necessary, therefore, that the moment
of inertia of all the parts rotating with the clutch when
the device affecting the change over from 3rd to 4th is in
neutral, should be very small.

Changing into lst and 2nd gear and reverse will be
made somewhat more difficult, because the internal gears will
rotate with the clutch.

The outstanding development from 1924 to 1928 has
been the application of the internal gear to the automobile
transmission. The general effect is to give a next-to-top
speed that is almost as silent as the direct with a sure and
easy shift between these two speeds.

The internal geared system has shown astonishing
resistance to wear and breakage. The remarkable wear and
strength factors of the internal gear make it ideal for this
field, whilethe easy gear shift makes it particulary attrac-

tive to the driver.

ELIMINATION OF GEARS

Numerous attempts have been made to eliminate
gears from the transmission and to use in their stead,
electric, hydraulic, or friction units. In using an electric
transmission, it is possible to diSpense with the flywheel,
clutch gears, the present starting motor and one set of
brakes.

In the hydraulic system, a hydraulic motor, a
pump, a control system and suitable piping are included.
Gear shifting has been one of the great drawbacks Of auto-
mobile Operation since the days of the first sliding gear
transmission.

A constant mesh transmission has some advantages:

1. Ease of gear shifting under any conditions

2. A.high degree of quickness Of Operation

3. Flexibility with very little divergence

from conventional designs

PRINCIPLES OF.AUTOMATIC OPERATION

All the engines have the characteristic that as
the torque load on them is increased, if no change is made
in the control or adjustment of the engine, its speed will
decrease; consequently it would be possible, by fitting the
engine with a governor, to connect this governor up to
shift the gears or to increase in some other way the trans-
mission ratio or torque multiplying ratio when the engine
speed decreases or vice versa. The car is fitted with a
device that affects shifting of the gears automatically by
a centrifugal governor.

When the car is at a stand still, the gear is in
neutral, and if the driver wants to start the car he engages
the lst speed by hand. As soon as the engine reaches a pre-
determined speed on this gear, the governor shifts the car
to second gear, and so on. If it is necessary to reduce
speed on account of traffic or other conditions, the operator
closes the throttle valve, thus reducing the engine speed,
and the centrifugal device then shifts automatically to a
lower gear. On the whole, it seems to be a simpler and
better plan to use the torque reaction to produce a change
in the transmission ratio when required.

the standard gear rear axle gear ratio varies from

3.7 to 5.1.

Transmission is replaced by hydraulic torque
converter in Leyland commercial vehicles.

Probably the first hydraulic torque converter
to be placed in production by an established firm was
offered by Leyland Motors in 193%. In this mechanism
all multiplication of engine torque for acceleration and
hill climbing is effected hydraulically, so that a mechan-
ical change gear is dispensed with entirely. Under ordi-
nary conditions of operation the drive is direct, the hy-
draulic mechanism being disengaged. Changes in torque
conversion ratio take place automatically, but the change
from hydraulic drive to direct drive is made by hand. Re-
verse is obtained through a Special reverse gear which is
combined with the double friction clutch and the hydraulic
mechanism in a unit correSponding in form and size to the
flywheel housing and transmission unit of mechanically
driven vehicles.

There are four control members:

1. The accelerator pedal

2. The brake pedal

3. The direct drive pick-up lever

4. The reversing lever

The latter normally remains in the position for
forward drive and is Operated only when it is necessary to

back up. A.double friction clutch is used.

8

With the clutch control mechanism in one position,
the engine crankshaft is directly connected to the main
drive shaft and the drive is therefore direct from crank-
shaft to prOpeller shaft.

In the Opposite position of the clutch control
mechanism, the engine crankshaft is connected to a hollow
shaft which carries the impeller of the hydraulic unit. There
are four essential elements in the bus type hydraulic torque
converter.

1. A double friction clutch which permits the
connecting of the engine either to the torque converter or
directly to the propeller shaft as required.

2. The hydraulic system of the converter

3. The free wheeling unit to permit over-running
of the converter

4. The reversing gear

;. The double clutch is operated by means of a
lever in the driver's cab, through a toggle mechanism. The
friction on clutches have very little work to do as the
vehicle is not being accelerated from a standstill to maxi-
mum Speed on a slipping clutch as_with mechanical transmission.
The engine can be idled with the clutch for the hydraulic
drive engaged and the car is then started and accelerated by
merely depressing the accelerator. Whatever slipping there
is up to the maximum speed attained through the hydraulic
drive takes place in the hydraulic unit. When the direct

drive pickup lever is moved to the direct drive position, the

9
vehicle is already moving at very nearly the Speed corres-
ponding to direct drive for the given engine speed and there
is, therefore, very little slippage at this clutch also.

As the change is made from hydraulic drive to
direct drive there is no interruption in torque and no cor-
responding loss of speed. As regards efficiency, it is claim-
ed that owing to the steady acceleration of a direct drive
and the provision of a free wheeling unit, this torque con-
verter compares favorably with mechanical transmission. The
hydraulic unit protects the transmission members behind it
against torsional vibration of the engine, and the engine
cannot be raced in running down hill at high speed.

.g. Torque converter consists essentially of the
combination of a centrifugal pump with a three stage hydrau-
lic turbine in the same housing. The pump impeller, which
is coupled to the crankshaft by means of the friction clutch
is similar in form to an impeller of the centrifugal pump
of the water cooling system. The turbine, which is connected
to the prOpeller shaft through the free-wheeling unit, con-
sists of a bladed rotor on which three separate series of
blades are fixed in such a way that they are separated by
two series of stationary blades fixed to the casing.

The housing is completely filled with fluid so
that when the engine power is being transmitted to the pump
impeller, the fluid is driven from the pump to the first set
of rotor blades, then through the stationary blades, where

the direction of flow is changed so that the fluid impinges

10

on the second set of rotating blades. Next the fluid passes
through the second set of stationary blades where it is
again redirected to impinge on the 3rd set of moving blades
after which it returns to the pump. Owing to the shape of
the blades and the fact that there are three sets of turbine
blades in series, the engine torque can be multiplied in
ratios up to 4.8 to 1. New fluid under certain conditions
is likely to gasify slightly and, to insure the removal of
the gas and the replacement of the gasified fluid, a perma-
nent leak to the reserve tank is provided through a control
value and fluid is drawn from this tank and added to the sup-
ply in the housing, as required, by an injector. To prevent
the fluid from reaching excessive temperature under condi-
tions of prolonged use of the hydraulic drive, a smaller
cooler is incorporated in the fluid circuit and located out-
side the chassis frame. The fluid used in the converter con-
sists of a mixture of lubricating oil and kerosene, or of
diesel engine fuel. ‘

2. Free wheeling unit. - The free wheeling unit
is mounted on the shaft driven by the turbine rotor and so
is effective only when the drive is through the hydraulic
unit. It has the effect of completely isolating the converter,
which later comes to rest immediately after its friction
clutch is disengaged,so that there is no hydraulic loss when
the drive is direct. The object of the free-wheeling is to

make coasting safe while the converter is engaged by its

friction clutch.

ll

.fl. The reversing gear is of the spur gear type
and is provided with a synchronizing device which facili-
tates engagement.

The Operation. - The engine is started up with
the operating (reversing) lever in the neutral position.

To start the vehicle this lever is pushed into the position
for forward motion, and then the engine is speeded up by de-
pressing the accelerator. The car gains speed and when it
has attained the usual top gear speed, the accelerator pedal
is slightly released and the control lever is pulled back
into the direct drive position. ‘Thereafter, the road speed
is controlled by the accelerator in the usual way.

When desiring to stOp the Operator pushes the COD!
trol lever forward and then stops the vehicle by means of
brakes. To restart, he releases the hand brake, presses the
accelerator pedal until top gear speed is reached and then

again pulls the control lever back.

12

THE DEVELOPMENT OF AUTOMATIC TRAKSMISSIONS

Several different types of transmission were used
on the early gasoline cars, including the individual clutch
type, the planetary type transmission, the sliding gear
transmission and the friction drive. .

.Aside from their lack of sufficient flexibility,
the chief objection to the early transmission was that they
were difficult to handle. It was believed that this diffi-
culty could be overcome by making the gear change or shift
automatic, and it is a noteworthy fact that the first car
with an automatic transmission was placed on the market as
far back as l904.

By 1910, the sliding gear transmission had come
into use on nearly all stock cars, the one important excep-
tion being the Ford Mbdel T, which retained the planetary
gear until 1928. There was no basic change in transmissions
during the second and third decades of the present century,
although a number of cars were equipped with so-called pre-
selective transmissions. This Operated by means of a small
lever carried on the steering post. The driver could at any
time set the mechanism for the change he expected to become
necessary next, and then when the time for the change arrived,
he would press down on the clutch pedal (or let up on the ac-
celerator pedal) and the gear would be changed in accordance
with the setting of the pre-selector lever, either by phys-
ical fcurce exerted on the clutch pedal, by a solenoid, or

by a vacuum cylinder.

13

Towards the end of the twenties the Warner Gear
Co. brought out its Hi-Flex Transmission, a four speed
design incorporating Internal Gears, and although this did
not prove a permanent success, it caused such a stir in
transmission circles that it must be considered as having
definitely reopened transmission problems. Since that time,
transmission gears have been made silent and the gear syn-
chronizing device was introduced, which practically elimi-
nated clashing and made shifting possible under all condi-
tions, with the result that the conventional sliding or
shifting transmission has become a rather satisfactory de-
vice: light and compact, highly efficient, easy to Operate,
silent in Operation, and ineXpensive to manufacture. A
continuously variable type, of course, would be preferable.

There seems to be only one really serious objec-
tion to the present type of conventional transmission, and
that is that it calls for the use of three pedals for the
control of the car. Two of these pedals, the accelerator
and the brake, must be Operated by the same foot and the
necessary shifting of the foot from the accelerator to the
brake pedal adds to the time lag in bringing the car to a
stop in an emergency. Besides it is inconvenient, and in
addition there is the possibility of the foot slipping from
the brake onto the accelerator pedal or of the accelerator
being depressed instead of the brake pedal by mistake. It
would therefore seem that a transmission which reduces the

number of pedals to two would be a real improvement.

14

.As we have suggested in the foregoing section,
transmissions may be divided into: (1) stepped, (2) con-
tinuously variable types.

Either of these may be controllable or automatic.
The driverin.every case has control Over the Speed of the
car by means Of the accelerator.

Infinitely Variable Transmissiqn_:

The first type Of automobile transmission which
made it possible to have an infinite number of graduations
in the transmission ratio was a friction disc drive. This
was regular equipment on four or five early cars, but it was
only motierately successful with the low engine powers of
that period, and it would be entirely impractical with our

modern passenger car engines Of around one-hundred HP.

HYDRAULIC TRANSMISSIONS

Another type of infinitely variable transmissions
on which a great deal Of work has been done with a view to
adapting it to automotive uses is the hydraulic. Hydraulic
transmissions naturally divide into two classes, hydrostatic
and hydrokinetic. In the former the working fluid is placed
under pressure and set in motion by a pump, usually Of the
multi-cylinder plunger type, and the fluid moved by this
pump acts on the pistons of a hydraulic motor. The rate at
which power is being transmitted by such a device is measured
by the product of the fluid pressure, and by the volume dis-

placed by the plungers of the pump in unit time. In order

15

to change the transmission ratio, the stroke of one of the
two elements is varied, usually that of the pump.

For instance, if the pump stroke is halved while
the Speed of rotation Of the pump, and the HP input remain
the same, then the pressure to which the fluid is subjected
will be doubled, and with twice the fluid pressure the torque
on the shaft of the hydraulic motor will be doubled while its
‘speed will be halved because of the lower rate of delivery by
the pump.

It seems that with the great increase in the power
of passenger car engines, such hydrostatic transmissions
have become entirely unsuitable for passenger car use. All
of the power transmitted is at all times converted first in-
to hydraulic power, and then converted back into mechanical
power, and the double conversion involves considerable losses.
It is rather doubtful whether such a transmission in automo-
bile use under normal conditions would show more than.75%
efficiency, and a loss of 25% Of the power in the transmission
would be highly objectionable.

In hydrokinetic transmissions, a fluid is set in
motion by a propeller provided with blades. In this case,
power is being transmitted by setting the fluid in motion by
the driving member, and than letting it spend its kinetic
energy on the blades Of the driven member.

If both driving and driven members are enclosed in
the same housing and the fluid passes directly from the

blades of the driving to those of the driven member, the

16
torque on the driven member will be not greater than that
on the driving member, and as the speed of the driven mem-
ber can never quite equal that of the driving member, we
have a device akin to the slipping clutch. In more correct
technical terminology it is known as a hydraulic coupling.
There is no slipping of gears or of dog clutches engaging
gears, and the fluid fly-wheel introduces a certain flexibil-
ity which prevents shocks. Although there is a slight loss
in the "flywheel" under normal driving conditions, it amounts
to only a few percent and it is therefore much more effic-
ient than the hydrostatic type of transmission.

The reason the fluid flywheel cannot increase the
engine torque is that it has no member on which any additional
torque could react. To Obtain an increase in torque a third
set of blades must be provided carried on a member that is
mounted rigidly on the engine or on the chassis frame.

Hydraulic couplings and hydraulic torque converters
can be combined with mechanical units in various ways to
secure automatic changes of gear ratio together with high ef-
ficiency of Operation under most driving conditions. All
multiplication of engine torque for acceleration and hill
climbing is effected hydraulically, and changes in "gear
ratio" take place automatically.

When the vehicle approaches the normal driving
Speed, the drivaésets the direct drive pick-up lever by hand
and therefore the drive is direct. Reverse is Obtained by

means of a special reversing gear which is combined with a

\0.‘

17

double friction clutch and a hydraulic mechanism. There
are four control members as follows: '

l. the accelerator pedal

2. the brake pedal

3. the direct drive pick-up lever

4. the reversing lever

The latter is normally in the position for forward
drive and needs to be moved only when it is desired to back
up. The direct drive position in the crankshaft is coupled
directly to the prOpeller shaft with the clutch control
lever in the opposite position. The crankshaft is connected
to the tubular shaft, which carries the prOpeller of the hy-
draulic torque converter. It is not necessary to accelerate
the vehicle with the friction clutch. The latter can be
fully engaged before the vehicle starts, and acceleration
is accomplished by means of the hydraulic unit by Opening
the throttle and Speeding up the engine. When the direct
drive pick-up lever is engaged the vehicle is already travel-
ing at a speed close to normal, and there is therefore a
minimum slippage and a minimum of wear and tear on the clutch
lining. This change is made without interruption in the
torque.

The hydraulic torque converter comprises a centri-
fugal pump and a three horsepower hydraulic turbine in the
_same housing. The turbine wheel is connected to the prOpel-
ler shaft through a free-wheeling unit whose object is to

disconnect the hydraulic unit from the drive mechanism when

18
the direct drive is used so that the prOpeller and turbine
wheel will not rotate and will not cause any hydraulic
losses. When the change to direct drive is made, the
Operator lets up on the accelerator pedal slightly.

The following points in connection with the design
of hydraulic transmissions are the results Of eXperience.

l. Idle fluid must be reduced to a minimum.
Fluid circulation must be as natural, easy, and short as
possible. The flow must be full, continuous, and free from
obstructions and undue changes throughout the whole circuit.

2. Action and reaction must be in close proxi-
mity consistent with working clearances. Parts moving re-
lative to each other should be separated by an Oil film of
up to .085 inch depending on location. Neglect of this may
lead to serious frictional loss. l

3. Good lubricating quality, lasting body free—
dom from acid and air are important.

4. The freezing point and the coefficient of
friction must be low, while the boiling point, flash point
and Specific heat must be high.

Sperm oil, winter grade, has proved the most sat-

isfactory working fluid under prolonged and exacting road

tests.

l9

OPERATION OF FLUID FLYWHEELS

Now that hydraulic couplings (fluid flywheels)
and transmissions are coming into use, an elementary ex—
position of their Operating principles is necessary. The
fluid flywheel or hydraulic coupling is a device in which
there is a liquid flow whenever at least one of its members
is rotating.

The device consiSts of two rotors, one connected
to the driving shaft, and the other to the driven shaft.
Both rotors are provided with vanes which form between them
cells or passages through which the working fluid may cir-
culate. The disc or rotor A connected to the driving shaft
is called the Impeller, and the rotor B connected to the
driven shaft, the runner. The impeller forms a housing of
annular shape which is completely filled with a liquid.

The driven shaft has a bearing in the impeller housing and
a suitable seal is provided to prevent escape of liquid
through this bearing.

Now let us assume that the impeller A is being
rotated by the engine and that runner B is being held from
rotation in some way, by engaging the brakes Of the car.
The liquid in the cells between the vanes of the impeller
will participate in the rotary motion of the impeller and
will be subjected to centrifugal force. Since runner B is
being held, the liquid in its cells is not subject to centri-

fugal force; hence the liquid in the impeller under the

2O

influence of the centrifugal force upon it, will leave the
cells of the impeller near the outer circumference and
enter the cells of the runner, and the liquid thus dis-
placed from runner will enter the impeller near the inner
circumference.

The liquid leaving the cells of the impeller,
owing to its rotary motion, impinges against the vanes of
the runner, thereby producing a driving force on these
vanes. A driving force on the vanes of the runner is equi-
valent to a torque on the shaft on which the runner is
mounted, that is, the driven shaft.

If the brake is now released, the low gear in
the transmission engaged, and the friction clutch let in
again, the torque on the driven shaft is less than the
torque which the engine is capable of developing, and the
runner will be set in motion. Between the cells of the im-
peller and those of the runner there is a certain free
space and this space is filled with liquid having a dual
motion, an angular motion around the common axis of the two
rotors, and superimposed upon this, a motion in the direction
parallel to the axis of the rotors.

When the driven shaft with its runner is rotating
in the same direction on the driving shaft with its impel-
ler, the liquid in the cells of the runner also rotates and
therefore is subject to centrifugal force, the same as the
liquid in the cells of the impeller. The direction of the
centrifugal force in each case is radially outward (drawing)

and the two forces therefore are in opposition to each

21
other in the fluid circuit, tending to cause the liquid to
flow in Opposite directions.

However, as long as power is being transmitted
from the driving to the driven shaft, this runner rotates
slower; consequently the centrifugal force on the liquid in
the cells Of the runner is less than the centrifugal force
on the liquid in the cells of the impeller and the differ-
ence between these two forces causes the liquid to flow
through the circuit. Power is being transmitted from the
driving to the driven shaft.

The question now arises as to the relation between
the torque on the driving and driven shafts, and between the
angular speeds of these shafts. Under steady driving con-
ditions at least, the torque on the driven shaft will always
be the same as the torque on the driving shaft in accordance
with the principle that to every action there is an equal
and Opposite reaction.

The torque which is transmitted from the impeller
to the runner is equal to the change of momentum Of the
liquid in the impeller (or in the runner). At the outlet
from the impeller, the momentum of the fluid is equal to the
radius Of the outlet in ft., by the tangential velocity of
the liquid at the outlet in ft. per second. Similarly, the
moment of the liquid at the inlet to the impeller is equal
to‘g x radius of impeller inlet x tangential velocity of the
liqgid at the inlet inihet per second. The difference be-

tween these two products is the change in momentum of the

22
liquid and therefore the torque transmitted in feet.

There is, of course, a certain amount of loss in
the coupling due to internal friction of viscous liquid and
skin friction between the liquid and metal surfaces. Con-
sequently, less power is received by the runner than is
conveyed from the engine to the impeller.

The difference between the speeds of rotation of
the impeller and runner is referred to as the SLIP and is a
measure of the power loss in the coupling.

During periods of acceleration there is a great
'deal of slip and consequently considerable loss. When the
car is at a standstill there is a 100 percent slip, and the
efficiency of the coupling therefore starts from zero. At
constant speeds the slip is about 2%. ,

The hydraulic coupling takes the place of the
engine flywheel and forms a flexible link in the transmis-
sion. It cannot replace the friction clutch in conjunction
with a transmission in which the deficient speeds are en-
gated by sliding gears into mesh.

While a hydraulic coupling will not multiply the
engine torque for acceleration and hill climbing, a very
similar device called hydrokinetic torque converter is capable
of doing this. To multiply the torque, it is necessary to
provide a third member called a Reaction member.

A is the impeller, B is the runner, C is the re-
action member. This device Obeys two fundamental laws:

(1) when running at constant speed, the active

torque and torque reaction must be equal and Opposite.

23

(2) The energy 1mported to a given mass of the
liquid by the impeller minus the internal loss attributable
to that mass, must be subtracted from it by the runner. NO
energy is absorbed by the reaction member as that member has
no motion.

The liquid in the cells of the impeller and
runner has a dual motion. It flows through the circuits in
planes passing through the axis of the converter and it ro-
tates about this same axis with the impeller and runner.

The liquid enters the cells of the impeller near
the axis of rotation and as it passes to the outlet from
these cells, which is further from the axis of rotation,
its velocity and its k. energy increases. The liquid retains
all of this k. energy as it enters the cells of the runner.
But in the cells of the runner the liquid flows toward the
axis of rotation and hence its kinetic energy is decreased.
The energy lost by the liquid in passing through the runner
is conveyed to the latter and by it to the driven shaft.

If the runner runs one-half as fast as the impeller, the
torque on it will be nearly twice the impeller torque. The
difference between these two torques will react on the re-
action member. The liquid presses against the vanes of the
reaction member in the same angular direction as it presses

against the vanes of the impeller.

24

HYDRAMATIC TRANSMISSION

With the adoption of hydramatic transmission,
Oldsmobile has done away with the conventional friction
clutch and clutch pedal. Still, the Operator has complete
control by means of the shift lever and the accelerator
pedal. The shift lever has four distinct positions:
neutral, high, low, and reverse, which are reached in the
order named by a continuous motion.

When the engine is being started, the shift lever
is in neutral. Finger tip shift direct from neutral to
hi is all the shifting required under normal conditions,
since the transmissions will shift automatically from lst
to 4th through the intermediate gears at predetermined road
Speeds varying with the throttle position, and with the
engine idling, the car will not move when in the driving
positions.

When the shift lever is shifted manually into
low, the transmission can Operate in lst and 2nd gears only.
It will shift automatically from lst to 2nd at a road
speed which varies with the throttle position. The low
position of the shift lever is to be used only in emergen—
cies on extremely steep grades and when it is desired to use
the engine as a brake. It is never used in normal operation.

A valuable feature of this transmission is that
the car can be locked positively on a grade when the engine

is dead by placing the shift lever in reverse. This is

25
effected by means of a spring loaded band on the rear unit
which locks the reverse unit.

The entire transmission is filled with a fluid
lubricant covered by precise specifications. The fluid
specified has been found satisfactory at a temperature of
1150F. down to -15°F.

An important feature of the mechanism is the in—
fluence of the throttle (or accelerator pedal) position on
the road Speeds at which gear changes take place. ,At part
throttle, any particular shift takes place at a lower car
speed than at full throttle. This, Of course, is highly de—
sirable, for when one wants to accelerate rapidly, the ac-
celerator is pushed far down, and the transmission then re-
mains in a given gear up to a higher road speed than it
otherwise would, which results in a higher rate Of accelera-
tion.

With the throttle fully Open the shift from:

let to 2nd occurs at round 15 m.p.h.

2nd to 3rd occurs at round 30 m.p.h.

3rd to direct drive occurs

at round 50 m.p.h.

The housing of the fluid coupling, which is sealed,
receives its actuating fluid directly from the transmission
housing, to which the fluid returns through a pOp-off valve
and a separate return line. This constant circulation of the

fluid prevents localization Of temperature effects and keeps

down peak temperature.

26

The transmission consists essentially of four
units: .

1. Within the engine flywheel, there is a fluid
coupling.

2. Then comes one behind the other -- 2 plane-
tary gear sets of the type comprising an internal ring
gear.

3. Planetary pinions in mesh with both the sun
gear and the internal gear. I

4. And finally in the rear part of the transmis-
sion housing there is a reversing gear also of the planetary
type-

Each Of the planetary units employed in forward
drive is provided with a brake band by means Of which one
of its members can be held from rotation, and with a clutch
by which the whole unit can be locked together to transmit
the power directly. The two units are referred to as the
front unit and the rear unit reSpectively.

The flywheel is bolted to the crankshaft while
the fluid coupling covering is bolted to the flywheel. For
lst speed, the sun gear Of the front unit is held from rota-
tion by a brake band. ‘ . -

Bands . . . . . . . both applied

Clutches . . . . . both released.

When the manual valve is moved to the “drive range"
position, it cuts Off the Oil that releases the rear servo,

allowing the spring to apply the band, and it directs oil

27
to the apply side of the front servo. With both front and
rear bands applied, the transmission is in lst speed.

The brake band of the front unit is applied by
Oil pressure. While the brake band of the rear unit is ap-
plied by both spring and hydraulic pressure, the fluid coup-
ling is kept filled under pressure by an Oil pump.

For 2nd gear:

Bands . . . . . . Front released and rear applied.

Governor pressure increases with vehicle speed to
a point where it will overcome the shifter valve Spring
and automatically Open the valve.

3rd speed:

Bands: -- Front applied. Rear released.

The 2 to 3 shifter valve Opens at a higher
vehicle Speed than the l to 2 valve because of greater
spring tension. The front servo apply pressure, then
applies the front unit band, causing this unit to go into
reduction. With the front unit in reduction and the rear
unit in direct drive, the transmission is in 3rd speed.

Bands: --- Both released.

In 4th gear both planetary units are locked and
the drive is direct, except for the slippage in the fluid

coupling.
Reverse:
Reverse anchor ------ locking reverse internal
gear
manual lever ------ reverse position.

Bands ---- Front applied. Rear released.

28

To obtain reverse, the manual valve is moved into
the reverse position with the following results:

a. It directs it to the front servo to apply the

Band.
0. It directs Oil to the rear servo to release
the Band.

c. It cuts Off the Oil to the govenor 80 there

can be no upshift in reverse.

Operation of the automatic feature depends upon the
Oil pumps which build up a pressure Of 80 p.s.i. There is a
large pump at the front end, Operated at engine Speed, whose
function is to produce pressure at starting so as to establish
actual running conditions. It will deliver 80 lbs. pressure
immediately. The second pump, a smaller unit, is mounted at
the rear and is driven by the output shaft, as is the govenor.
The rear pump picks up the pressure as soon as the car moves,
permitting the front pump pressure to drOp to around 20 p.s.i.

The hydraulic control system:

This system supplies the Oil pressure necessary to
actuate the clutch pistons and brake bands of the planetary
units. Oil is admitted to the various cylinders at the prOper
time by a system of balanced valves. Its pressure balances
some variable force. In the case Of the throttle valve, a
spring pressure is balanced, while in that of the govenor
valve the forced balanced is centrifugal.

Oil is admitted to the body of the govenor valve

through the 80 lb. line from the pump. The govenor is driven

29
from the transmission output shaft and, as it Spins, the
centrifugal force so positions the valve, that a port is
Opened and some Of the Oil is admitted to the valve, with the
result that a pressure is built up which opposes the centri-
fugal force acting on the valve. This results in a govenor
pressure which increases with car speed. This govenor pres-
sure is applied to one end of a shifting valve, as for in-
stance the valve which makes the shift from 3rd to 4th gear.
To the Opposite end Of this valve is applied a fixed Spring
pressure and another variable hydraulic pressure, known as
the throttle valve pressure. This latter pressure is deter-
mined by the position Of the throttle and is regulated by
another balanced valve.

When the force exerted on the 3rd to 4th valve by
the govenor pressure exceeds that exerted on the Opposite
end by the throttle valve pressure and thisspring pressure
combined, the valve shifts and oil is allowed to pass to the
front unit clutch pistons and the brake release piston of
the front unit servo. This shift to 4th gear occurs at about
20 m.p.h. at light throttle. If the accelerator pedal is de-
pressed further, the throttle valve pressure is increased;
consequently the govenor pressure must be raised to a higher
value before the shift can take place. This can be done only
by raising the car Speed. Therefore, by varying the throttle
Opening, the Speed at which the shift from 3rd to 4th occurs
can be varied within a wide range. ‘At full open throttle,

the shift is made at about 65 m.p.h.

30

In order to Shift down from 4th to 3rd at Speeds
below 65 m.p.h., it is necessary that the force drive to
throttle valve pressure and spring pressure combined exceed
the pressure due to the govenor. Under these conditions oil
pressure is cut Off from the clutch pistons and brake release
piston and directed to the brake applying piston; Opening the
throttle valve provides the necessary force on the shifting
valve to accomplishthis change from 4th to 3rd at Speeds
between 20 and 65 m.p.h.

The govenor really consists of two valves, one Of
which builds up pressure very rapidly while the other builds
it more slowly. This results in a greater flexibility of
control than is possible with a single stage govenor. Shifts
between lst and 2nd gear are actuated by that stage of the
govenor in which the pressure is built up more rapidly, and
shifts between 2nd and 3rd and 3rd and 4th make use of both
stages.

The reduction in the creeping tendency may be ex-
plained as follows: When the car is at'a standstill, with
the Shift lever in driving position and the engine idling,
the transmission is in lst gear. The only reason the car is
not moving (if the brake is released) is that the fluid
coupling at the low Speed of the engine does not produce suf-
ficient torque to set the car in motion. The torque trans-
mitted by the fluid coupling_of the hydramatic drive is very
low because with the transmission in lst gear, the impeller

of the coupling turns at only about 7 times the crankshaft

31
speed and, as the torque of the Speed, it is only about 1/2
what it would be if the coupling were driven directly from
the crankshaft.

An important advantage of the fluid coupling in
the transmissiOn is that it will even out torsional distur-
bances.

The front unit brake band is now applied by Oil
pressure instead Of by spring pressure.

The rear unit band is actuated by a combination of
spring and Oil pressure. It is applied and held by Spring
and Oil pressure and released by oil pressure.

In the clutch mechanism there are now six pistons
instead of three.

Another innovation is the use of hydraulic govenor

driven by the output shaft of the transmission.

32
CADILLAC'S NEW HYDRAMATIC TRANSMISSION

Cadillac's new hydramatic transmission is the same
as Oldsmobile transmission. It may be recalled that a hy-
dramatic is a 4 speed transmission employing planetary gear
units, combined with a fluid coupling which is used in com-
bination with a low reduction rear axle. It is completely
automatic, eliminating the clutch pedal and gear shift lever,
and the need for their Operation. It eliminates jerky starts,
quiets the engine by lowering its Speed of Operation, and
damps out vibration and shock. Acceleration and hill climb-
ing ability are increased, and the car is said to have better
traction on slippery surfaces. The automatic transmission
is claimed to reduce fuel and Oil consumption and wear and
tear on the engine.

The direct design difference is that the intermed-
iate planetary unit located substantially at the center of
the housing is a 2 step instead Of a single step reduction
gear.

The manual control consists of a small lever and
indicator mounted on top of the steering column beneath the
steering wheel. This indicator shows the positions: neutral,
Hi, Lo, and reverse.

For all normal driving, the Hi position is used
when the car is started in this position and the transmission
shifts automatically through the four Speeds. When set in Lo,

3rd and 4th speeds are locked out so that the transmission

33
reamins in either lst or 2nd gear, making it possible to
use the engine as a brake when descending hills.

TO start the car, the Operator starts the engine
with the gear selector in neutral, selects the direction by
placing the selector lever in either reverse or hi position

and then steps on the accelerator.

10.

ll.
12.

1'3.

1923,
1924,
1925,

1926,

1927,

1928,

1930,
1932,
1935,

1936,

1937,

1948,

34

‘Automotive Industries

Chandler adOpts new type of gear set for 1924
model. New transmission invented in EurOpe.
Weiss variable speed transmission.

Unconventional transmission by P.M. Heldt.
Ohio four speed transmission.

Burness 4 Speed planetary transmission. Silence
of internal gears accounts for interest in 4
Speed transmission
Detroit gear sets. Planetary gear type trans-
mission by Ford. Internal gear outstanding trans-
mission developed by S. 0. White. 5 COTTA Trans-
mission.

British fluid transmission devices by M.W. Bourdon.
Improved planetary transmission by P.M. Heldt.

4 Speed constant mesh transmission with direct
drive by Joseph Geschelin.

Bendix hydro mechanical transmission by Adiel Y.
Dodge.

The develOpment of automatic transmission.
Fluid flywheel by P.M. Heldt. Torque converter
by P.H. Heldt.

Buick dynaflow transmission by Joseph Geschelin.

L

Y
1 USE ONLY
9w”
3.; :- H

M " —~.- £64321“

 

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