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0-169

K
M A“ l-‘-._ “—45--“ ‘ pun.- - l _‘l A

This is to certify that the

thesis entitled

Characteristics and Types of Hydro-
dynamic Torgus Converters.

presented by

Gordon Wsng

has been accepted towards fulfillment
of the requirements for

Ldegree ill—Mechanical Engineering

Major professor

Date May 22: 1951

 

 

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PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before one due.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

MSU Is An Affirmative Action/Equal Opportunity Institution
emana-oc

 

CHARACTERISTICS AND TYPES OF HYDRODYNAMIC TORQUE CONVERTERS

BY

Gordon Wang

A THESIS

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

1951

TH E'SIF

/:17 /57

ACKNOWLEDGMENTS

The writer wishes to eXpress his sincere apprecia-
tion to Professor G. W. Hobhs_for his timely advice and
guidance throughout this study.

Gratitude also is exPressed to Professor J. N.

Windburne for his critical reading of this manuscript.

255877

 

 

 

CONTENTS

PAGE
PART 1 CHARACTERISTICS OF HYDRODYNAMIC TORQUE

CONVERTERS
CONSERVATION OF TORQUE . . . . . . . . . . l
VELOCITY DIAGRAMS FOR THE PUMP . . . . . . 3
VELOCITY DIAGRAMS FOR THE TURBINE . . . . 6
VELOCITY DIAGRAMS FOR THE REACTION

MEMBER . . . . . . . . . . . . . . . . . 7
TORQUE AND ENERGY TRANSFER AT THE

PUMP . . . . . . . . . . . . . . . . . . 7
TORQUE AND ENERGY TRANSFER AT THE

TURBINE . . . . . . . . . . . . . . . . 9
ENERGY LOSSES ACROSS THE PUMP . . . . . . ll
ENERGY LOSSES ACROSS THE TURBINE . . . . . 12
ENERGY LOSSES ACROSS THE REACTION

MEMBER . . . . . . . . . . . . . . . . . 13
ENERGY EQUATION . . . . . . . . . . . . . l4
CHARACTERISTICS OF TORQUE CONVERTER . . . 15
DESIGN FACTORS FOR REDUCING FRICTION

LOSSES . . . . . . . . . . . . . . . . . 18
DESIGN FACTORS FOR REDUCING SHOCK

LOSSES . . . . . . . . . . . . . . . . . l9

DESIGN’FEATURE FOR REDUCING SHOCK
LOSS AT THE PUMP . . . . . . . . . . . . 21

 

 

 

 

PAGE
DESIGN FEATURE FOR REDUCING SHOCK

LOSS AT THE REACTION MEMBER . . . . . . . 23
IMPROVEMENT OF CONVERTER PERFORMANCE

BY FREEWHEELING UNITS . . . . . . . . . . 25

PART 2 TYPES OF HYDRODYNAMIC TORQUE CONVERTERS

TORQUE CONVERTER IN CHEVROLET POWER-

GLIDE TRANSMISSION . . . . . . . . . . . 27
TORQUE CONVERTER IN BUICK DYNAFLOW

TRANSMISSION . . . . . . . . . . . . . . 29
TORQUE CONVERTER IN MERCURY-FORD

TRANSMISSION . . . . . . . . . . . . . . 3l
TORQUE CONVERTER IN PACKARD ULTRA-

MATIC TRANSMISSION . . . . . . . . . . . 32
TORQUE CONVERTER IN STUDEBAKER TURBO-

MATIC TRANSMISSION . . . . . . . . . . . 34

PART 1

CHARACTERISTICS OF HYDRODYNAMIC TORQUE CONVERTERS

 

CHARACTERISTICS OF HYDRODYNAMIC TORQUE CONVERTERS

A hydrodynamic torque converter consists of es-
sentially a pump wheel connected to the input shaft, a
turbine wheel connected with the output shaft and a re-
action member ring fixed or clutched to a stationary con-
verter housing. Fig. 1 shows the arrangement of pump,
turbine and reaction member for a typical torque conver-
ter. A fluid is used as a medium of torque and energy
transfer which recirculates in a closed path formed by the
converter elements.

CONSERVATLON OF TORQUE. The velocity of any fluid parti-
cles circulating in the annular ring has two components:
(1) Circumferential and (2) Annular. The circumferential
component is perpendicular to the plane of the annular
ring, and the annular component is in the plane of the
annular ring which determines the rate at which the fluid
recirculates.

The angular momentum of a fluid particle about an
axis is equal to the product of its weight, its distance
to the axis and its circumferential component. The angu-
lar momentum is designated to be positive when the cir-
cumferential velocity of the fluid particle is in the
same direction of the motion of the pump, and it is nega-

tive when the circumferential velocity of the fluid is in

 

Reaction‘Member

  
  

         
 

 

Turbine
\\
e'.
.0"
Pump 3? ’
\ : J a
. 0
~‘ / 0'
§‘ t A
I at t o I
: °o ‘
E R3
5 1
R2 3 A
a 1
o 4_,“ },i-

  

/
Axis of Rotation

 

Converter Housing

 

Fig. l Hydrodynamic Torque Converter

the opposite direction of the motion of the pump.

The mechanical torque exerted upon the wheel by
the fluid is the difference of angular momentum of the
fluid entering and leaving the wheel per unit time.

The angular momentum of the fluid leaving the pump
is larger than that entering it due to the energy input
at the pump, therefore the torque on the pump, which op-
poses the motion of the pump, is negative.

On the other hand, the turbine absorbs the kinetic
energy of the fluid thereby the angular momentum of the
fluid entering the turbine is larger than that leaving
the turbine, consequently the torque exerted upon the
turbine bears a positive sign which assists the motion
of the turbine. In many cases, the angular momentum of
the fluid leaving the turbine is very low and even changes
its sign into negative: that means the fluid has reversed
its motion in the circumferential direction. If there is
no reaction member, as in the hydraulic fluid coupling,
the pump has to raise the negative angular momentum to a
certain positive value. It would require the entire
engine torque to stop this backward rotation when it hits
the entrance to the pump. And there would be nothing left
to get the fluid reenergized into a positive rotation.

To correct this difficulty, the reaction member

consisting of a set of stationary curved vanes is in-

 

 

 

stalled between the turbine exit and pump entrance.

These vanes are properly shaped to receive the backward
spinning fluid, bring it to a stop and then to direct it
to a forward rotation. The angular momentum of the fluid
leaving the reaction member is therefore larger than that
entering it. A negative torque results which tends to
rotate the reaction member opposite to the motion of the
pump.

Since the total change in angular momentum about
the axis of rotation is nil in a complete circulation,
the resultant torque exerted upon the wheels therefore is
also nil. The torques on the pump, turbine and reaction

member are Tp, Tt and Tr respectively. Then

-Tp+Tt-Tr=0

or, Tt = Tp + Tr (1)

Thus the turbine torque is equal to the engine or
pump torque augmented by the torque reaction of the re-
action member.

VELOQITY DIAGRAMS FOR THE PUMP. From the foregoing dis-
cussion, only the entrance and exit of the wheels are con-
sidered important. Therefore, a knowledge of the velocity
relations at the entrance and exit of the wheels is

necessary in order to analyze the torque converter. The

diagrams showing the velocity relations at the entrance

and exit of the wheels are called velocity diagrams.

(Refer to Fig. l.) A central portion of the annu-

lar ring M is chosen as the characteristic section of the

torque converter. It is called the mean stream layer.

Before discussing the velocity diagrams for the

pump, the different parameters necessary to construct the

velocity diagrams are given the following notation:

Q, flow rate of the fluid, cu. ft. per sec.

D, density of the fluid, lb. per cu. ft.

WP,

R1,

R2,

Cg,

Speed of the pump, radians per sec.

mean radius between the pump entrance and
reaction member exit, ft.

mean radius between the pump exit and turbine
entrance, ft.

entrance area of the pump, or exit areas of the
reaction member, sq. ft.

exit area of the pump, or entrance area of the
turbine, sq. ft.

absolute velocity of the fluid between the
reaction member and the pump, ft. per sec.
absolute velocity of the fluid between the

pump the turbine, ft. per sec.

Vpl’ relative velocity of the fluid in regard to

the pump at entrance, ft. per sec.

sz, relative velocity of the fluid in regard to
the pump at exit, ft. per sec.
Bpl’ blade angle of the pump at entrance, deg.
sz, blade angle of the pump at exit, deg.
Vshp’ shock velocity at the pump, ft. per see.
thp' relative velocity of the fluid in regard to
the pump at entrance before the guiding effect,
ft. per sec.
g. the gravity constant, 52.2 ft. per sec. per sec.
The velocity diagrams at the pump exit will be dis-
cussed first. (Refer to Fig. 2.) The fluid leaves the
pump with a relative velocity V

2 at an angle B 2 with the

P P
motion of the pump. And the velocity of the pump at that
point is Wth. The resultant force 02 is the velocity of

the fluid at the pump exit. The annular component of 02
is Q / A2.

.There is a slight difference at the pump entrance.
(Refer to Fig. 3.) The fluid leaves the reaction member
at an absolute velocity Cl. The velocity of the pump at
the entrance is WpRl, therefore, the relative velocity
of the fluid before meeting the blade is thp. However,
upon entering the pump the fluid changes its relative
velocity from thp to Vpl due to the guiding effect of
the blade. Bpl is the blade angle. The vectorial

difference of thp and Vpl is Vshp: which is called shock

K .

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velocity. Except for one set of conditions, the blade
entrance is not built to receive the fluid smoothly, and
the shock velocity exists.
VELOCITY DIAGRAMS FOR THE TURBINE. Figs. 4 and 5 show
the velocity diagrams at the turbine entrance and exit
reapectively. The following notation is given:
Wt. Speed of the turbine, radians per sec.
R5, mean radius between the turbine exit and re-
action member entrance, ft.
A5, exit area of the turbine of entrance area of
the reaction member, sq. ft.
Vt2' relative velocity of the fluid in regard to
the turbine at entrance, ft. per sec.
Vt3, relative velocity of the fluid in regard to
the turbine at exit, ft. per sec.
039 absolute velocity of the fluid between the
turbine and the reaction member, ft. per sec.
Bt2' blade angle of the turbine at entrance, deg.
BtS' blade angle of the turbine at exit, deg.
(Refer to Fig. 4.) The fluid leaves the pump with
an absolute velocity C2, The velocity of the turbine at
that point is WtRZ’ therefore the relative velocity of
the fluid in regard to the turbine is tht‘ But the guid-
ing effect of the blade changes tht to V 2 at an angle

P
Bt2° The shock velocity is Vsht’

 

 

SIDE VIEW

 
 

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TOP VIEW

Fig. 4

Velocity Diagram at the Turbine Entrance

 

 

 

 

 

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7

At the exit of the turbine (refer to Fig. 5.) the
fluid leaves the turbine with a relative velocity VtS‘
The sum of Vt3 and the velocity of the turbine at that
point th5 is C3, the absolute velocity of the fluid.
That the circumferential component of the velocity of
the fluid changes direction after passing through the
turbine is clearly shown.
VELOCITY DIAGRAMS FOR THE REACTION MEMBER. (Refer to Fig.
6.) For the stationary reaction member the fluid enters
the wheel with an absolute velocity C3. Since the wheel
is stationary, the absolute velocity C3 equals to thr
the relative velocity of the fluid. The guiding effect
of the blade changes thr to vshr’ the shock velocity.

(Refer to Fig. 7.) The fluid leaves the wheel with
a relatively velocity vrl at Brl' Since the reaction is
stationary, the relative velocity Vrl equals to C3, the
absolute velocity of the fluid between the reaction mem-
ber and the pump.

The reversal of direction of the circumferential
component of the velocity of the fluid is shown.
TORQUE AND ENERGY TRANSFER AT THE PUMP. Considering the
interaction of the fluid with the pump. (refer to Fig. 2.)
the circumferential velocity of the fluid at the pump
exit is the sum of the velocity of the pump at that point

WpRgplus the circumferential component of the relative

'd‘

 

 

 

 

 

 

 

 

 

 

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fluid velocity 9 cothe, since the annular velocity of
A
the fluid relatige to the pump is Q / A2.
The angular momentum of the circulating fluid

across the exit section of the pump per unit time is

129 ( WPR2 + Q coth2 ) R2 ft-lb. per sec.
g A2
The angular momentum of the fluid per unit time
entering the pump is likewise the angular momentum of the
fluid per unit time across the exit section of the
stationary reaction member, 1. e.,
23 (‘Q cotBrl ) Rl ft-lb. per sec.
8 Al
The torque exerted on the pump is the difference
of the angular momentum of the fluid leaving and enter-

ing it, therefore

T =IQQ ( WpRg + Q coth2 R2 - Q cotBrl ) ft-lb
8 A2 . A1 (2)

Or,
_. 2
T - 1(1pr + K2Q ft~lb (2)

where, Kl = p a:
e

K =.Q ( cotB R - cotB )
2 g -EE-p2 -]E-rl

The power input at the pump is

Pp = Tpr = ( Klpr + KBQZ ) WP ft-lb per sec.
(3)

At constant flow rate Q, the torque on the pump in-
creases directly with the Speed, while the power input
varies as a parabolic function of the pump Speed. While
at the constant pump speed WP,
power input varies as a parabolic function of the flow

both the pump torque and

rate.

TORQUE AND ENERGY TRANSFER #AT THE TURBINE. The driving
torque on the turbine wheel equals the difference be-
tween the entrance and exit angular momentum of the fluid
per unit time. The entrance fluid angular momentum of
the fluid per unit time to the turbine is the exit fluid

angular momentum per unit time from the pump, namely

‘29 ( WPRZ +.% COthz ) R2 ft-lb per sec.
8
2

The exit angular momentum of the fluid per unit

time from the turbine is

29 ( thS + _O_ cotBts ) R3 ft-lb per sec.
g A5

The driving torque exerted by the fluid on the

turbine is therefore,

lO

 

2 . 2,
A2 A3 (4)
Or,
2
where,
2
K = D R
l g 2

K5 = 2 ( R2 COthz - Rs COtBtS )

g .______
A2 A3

2
4 . g 3

The power transfer between the fluid and the tur-

bine is

Pt = rsws = ( KlQWp + KSQZ - K4th ) wt ft-lb per sec.
(5)
If the pump speed in constant, at any given turbine
Speed Wt, both the turbine torque and power output varies
as a parabolic function of the flow rate. For any given
flow rate Q, the turbine torque decreases with increase
of turbine speed, and the power output varies as a para-

bolic function of Wt.

 

 

 

 

11
To find the relation of the power output Pt and
turbine speed Wt for constant pump speed W and constant

P
flow rate Q, equations (4)' and (5) can be rewritten:

Tt = M - NWt ft-lb - (6)
Pt = ( M - th )wt ft-lb (7)
where,

M = 1(1qu + K3Q2

N=K4Q

The maximum turbine torque is M when Wt is zero,
or, in other works, when the turbine stalls.
To find the turbine speed at maximum output. Let

the first derivative of P1: with respect to Wt to zero,

43-
dwt

so, Wt = _M.

Substituting this value of Wt into equation (6)

gives T equals to M / 2. This means that the stalling

t
torque is just twice the torque developed at the turbine
Speed when maximum power output occurs.

ENERGY LOSSES ACROSS THE PUMP. The fluid flow through

various passages is subjected to different losses. These

12

losses are divided into shock and friction losses. Shock
losses are suffered from a wrong angle entrance into the
blades and roughly varies with the square of the shock
velocity. While the friction losses are suffered through
the path of the converter assuming that the fluid enters
the blade shock free, and are prOportional to the square
of the exit relative velocity of the fluid.

The energy losses across the pump will be discussed

first. Refer to Fig. 5 and 7, the shock velocity vshp is
equal to
‘9 cotBrl -‘Q cothl - prl ft-lb per sec.
A A
l 1
Therefore, the shock loss at the pump
L =‘_Q (.Q cotB -.Q cotB - )2
shp r1 pl p81
2g A1 A1
ft-lb per sec. (8)

In the equation (8), the Shock coefficient is unity.
The exit relative velocity at the pump exit of the

fluid is Q, csch2 (See Fig. 2), the friction loss

A2
L = fD93 ( cscB )2 ft-lb per sec (9)
fp 2g __K_p2
2

where, f = .2 roughly
ENERGY LOSSES ACROSS THE TURBINE. For the Shock loss,

refer to Fig. 2 and Fig. 4, the shock velocity at the

15

turbine entrance Vsht is

+ .. -
WPR2 %,coth2 th2 fig cotBtz ft. per sec.
2

The shock loss,

2
= . + .. -
Lsht _D_9_ ( wa2 Qcothz th2 g cotBtz )

ft-lb per sec. (10)

The relative exit velocity of the fluid 15.9 csth5,

A
(See Fig. 5). The friction loss 2
_ 5 2
L - D9 ( cscB ) ft-lb per sec. (11)
ft -——-t5
2g A:5

ENERGY LOSSES ACROSS THE REACTION MEMBER. Refer to Fig.

5 and 6, the shock velocity at the reaction member entrance
Vshr is

WtR3 + Q, cotBt3 -.Q cotBr3 ft per sec.
Therefore, the shock loss

2
L5hr - D9 ( thS +.Q cotBt3 -.Q cotBr5 )

ft-lb per sec. (12)

And from Fig. 7, the relative velocity of the fluid

at the reaction member exit is.Q cscBrl. The friction
A
loss at the reaction member is 3

l4
2

Lfr = ng5 ( cscBrl ) ft-lb per sec. (15)
8 A1

ENERGY EQUATION. According to the law of conservation of
energy, the power input at the pump is equal to the sum
of the power output at the turbine and the losses across

different wheels. Therefore,

Pp = Pt + Lshp + pr + Lsht + Lft + Lshr + Lfr

ft-lb per sec. (14)

Substituting Pp, Pt and different losses from the

foregoing sections and simplifying gives:

wz ( R2 - Rl ) + wt ( R3 - R2 )
2s 2s

=.Q WpRlcotEpl / Al - WSRSCOtBrS / A5

+'Q? f cscB2r1+gcotBrl ~ COthi)2

2s
f cscB2 + ( c tB tB )2
——————r1.————§9-r1 :_£2_.p1
A2

f cscfifis + ( cotBts - coth3)2
2

A (15)

5

15
CHARACTERISTICS OF TORQUE CONVERTER. Torque ratio is
defined as the ratio of the turbine torque to pump torque,
or

2
KQW +KQ-KQW
Torque ratio = Tt / Tp = 1 P 5 4 t

 

 

. 2
2
where, K "' DRE
1
g
K2 ='2 (cotB 2 R2 - cotBrl )
g A2 A1
K = D ( chothz - RECOtBtS )
5 5 A2 A3
2
K = D R
4 _.
g 5

The overall efficiency of the torque converter is

given by the equation:

2
(KQW +KQ-KQW)W

 

p 2
( Klwp + KZQ ) wp
Equation (15) can also be expressed as an implicit
function of variable WP’ Wt, Q ( and the blade angles or

radii if they can by made to vary ) :

F ( WP. Wt, Q ) s O (18)

16

Only two of the variables WP’ W and Q are con-

t
sidered to be independent. If W and W are chosen as

P t
independent variables, Q can be calculated by equation.
(18). By substituting the values of Wp, Wt and Q into
the torque and energy or power equations derived in the
previous sections, the characteristics of a torque con-
verter of certain design can be found.

If the pump speed WP is kept constant, then the
circulation rate Q varies with the turbine speed Wt
according to the equation (18) or (15). The turbine
torque Tt modified from a linear relation with the tur-
bine Speed Wt. And the pump torque Tp cannot be constant
throughout the range of the turbine speeds, and must vary
with the turbine speed.

If the pump torque T is kept constant, then

P
Tp = KleQ + K2Q2 = constant
or,
Q = - 1(le + (Kiwi + 4K2Tp )1/2

 

2K2

On substituting in the equation (18) or (15), WP
is directly related with Wt‘ At constant pump torque,
the pump speed increases nearly linearly with the turbine

Speed.

17

However, if the pump speed W? is constant, the
characteristics of the torque converter are not greatly
modified by assuming a constant flow rate Q for a wide
range of turbine speed Wt. Since the pump Speed WP and
flow rate Q are assumed to be constant, this implies
that the power input Pp and pump torque Tp are constant.
The efficiency of the torque converter therefore will be

Pt ( M - wwt )‘wt

e = _, = (19)

Pp prp

where, m = KlQWp +~K5Q2
N = K4Q

The efficiency, assuming a constant flow rate, as
Shown in equation (19) reaches a maximum when Wt equals
to M / 2N or the rated Speed, and falls to zero when Wt
equals to zero and M / N.

One difficulty with a direct application of the
torque converter is the rapid drop of efficiency with in-
creasing overSpeed relative to its rated speed.

Fig. 8 shows the torque and efficiency curves at
constant pump speed W? for a wide range of turbine speed.
The flow rate Q increases as the turbine speed either de-

creases below or increases above the rated Speed, thereby

the correSponding output torque and efficiency are higher

than that of assuming a constant flow rate.

18

However, the increase of torque ratio and efficiency
due to the increaseof flow rate is checked by the in-
crease of friction loss and shock loss at both the lower
and higher speeds. Therefore, a thorough understanding
of the nature of these losses is indispensable in order
to decrease these losses and thereby increase the per-
formance of the torque converter.
DESIGN FACTORS FOR REDUCING FRICTION LOSSES. Equations
(9), (10) and (11) eXpress the friction losses at dif-

ferent wheels as follows:

5
L = fDQ cschz )2
5 2
5
L = fDQ ( csth3 )2
ft -———- -———-—-
2g A3
3

“T

The friction coefficient f depends on the blade
and shell wall friction, curvature of the blade, and the
viscosity of the circulating fluid. Under most favorable
conditions: smooth surface finish on the blades and shell
wall, uniform rate of change of curvature of the blades,
and minimum viscosity of the fluid, the friction coeffi-
cient can be made as low as 0.08. In most cases, the

friction coefficient lies between 0.15 to as high as 0.25.

19

The relation of the exit blade angle to the
friction losses is clearly shown in the equations. In
order to reduce the friction losses, the angle should be
small. The annular cross-sectional area also affects
the friction losses, the larger the area, the smaller
the losses.

The most important single factor affecting the
amount of friction losses is the rate of circulation of
the fluid Q. When the turbine speed is low, the flow
rate is extremely high. Therefore the highest friction
losses are suffered when the turbine speed is low, es-
pecially when the turbine stalls.

The fluid density also affects the friction losses
as indicated by the equations. However, its effect is
so small, that the fluid with maximum density and mini-
mum viscosity is used in order to carry more energy per
unit volume of the fluid. In other words, the converter
can be made smaller with heavier fluid.

DESIGN FACTORS FOR REDUCING SHOCK LOSSES. Shock losses
are responsible for the rapid decrease of the converter
efficiency at low and high turbine Speeds. In turbines
with the wheels arranged in the pump, turbine, reaction
member order, the highest shock loss is at the reaction
member entrance, less at the pump entrance and negligible

at the turbine entrance.

20

Assuming the pump torque being constant, the flow
rate Q is highest when the turbine Speed is zero. As
the turbine speeds up, the flow rate decreases until it
becomes minimum at the rated turbine Speed, and the flow
rate increases as the turbine overspeeds. The pump speed,
however, increases linearly at a slow rate with the in-
crease of the turbine speed. _But when the turbine speed
is over the rated value, the pump speed increases rapidly.

The nature of the entrance relative velocities thp’
tht and thr relative to the turbine speed will be dis-
cussed separately.

The entrance condition at the turbine will be dis-
cussed first. Fig. 9a is the velocity diagram at the
pump exit when the turbine stalls, and Fig. 9b is the
velocity diagram at the turbine entrance. As the turbine
speed increases, the velocity diagram at the pump exit
is changed, as shown in Fig. 9c. The flow rate Q reduced
due to the increase of turbine speed, and the fluid
velocity 02 rotates clockwise as compared to 02 in Fig.
9b. However, at the turbine entrance, the effect of
change of direction of the fluid velocity is compensated
for by the motion of the turbine which tends to make the
entrance relative velocity tht in the same direction as
V ht in Fig. 9b. Consequently, the shock losses at the

w
turbine is small and can be neglected.

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21

But the situations at the pump and reaction member
entrance are different. In the following section, the
shock loss at the pump entrance and the method of reduc-
ing it will be discussed.

DESIGN FEATURE FOR REDUCING SHOCK LOSS A; THE PUMP. Fig.
10a is the velocity diagram at the reaction member exit,
and Fig. 10b is the velocity diagram at the pump entrance
when the turbine stalls. As the turbine speeds up, the
velocity diagrams at the reaction member exit and pump
entrance are shown in Fig. 10c and Fig. 10d respectively.
The smaller flow rate and higher pump speed cause the
relative fluid entrance velocity thp shift to the left
side as compared with thp in Fig. 10b. Fig. lOe shows
the change of direction of thp the relative entrance
velocity at low and high turbine speeds. At low turbine
speed, especially when the turbine stalls, the value of
rate of fluid flow is high, and the shock loss is at its
maximum.

In order to reduce the shock loss at the pump
entrance at low turbine speed, the pump is divided into
two pieces. Refer to Fig. lie, the secondary pump 8 is
attached to the primary pump P by roller clutches. S is
permitted to turn faster than P in the direction of
motion of P, but never lags behind due to the one way

action of the roller clutches.

 

 

 

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22

At low turbine speed, the fluid tends to throw a
positive torque on the pump, and as a result the secondary
pump freewheels ahead of the primary pump. When the tur-
bine speeds up, the direction of the flow velocity of the
fluid relative to the pump changes, and the secondary
pump is locked to the primary pump as the flow direction
passes the blade angle.

Fig. 11b, c, d, and e show the velocity diagrams
at the pump entrance without and with freewheeling units.
Z being the difference of circumferential velocities of
points p and s on P and S reSpectively.

The shock loss at S without freewheeling is

2

L = vs‘hp

shp 2g

 

With freewheeling unit, the shock loss at piece
S is (See Fig. llc)
2
r
2%

 

And the shock loss at piece P is

.23

22

The total shock loss with freewheeling unit is,
then

23
2 2
shp r

 

2%

The percentage in Shock loss saving with freewheel-
ing unit at a velocity differential Z is

 

 

2 2
L - L‘ 2 v z R - z 1 + ( _R )
Shp Shpioo = Shp F1 r1 100
Lshp V2
shp (20

Equation (20) can also be eXpressed as

I
L - L R Z Z R
shp shp = 2 _ ( )2 1 _ ( -l )2
L Vshp r

HI
.<

shp shp

(20)1

The saving is a function of Z/ Vsh , and the radius

P
ratio Rl/r. It is highest when Rl/r equals to l, i.e.,
when the entrance radius at P is equal to the entrance
radius at P'.

DESIGN FEATURE FOR REDUCING SHOCK LOSS AT_THE REACTION
MEMBER. The shock loss at the reaction member is the
highest compared with those at the turbine and at the
pump. Fig. 12a shows the velocity diagram at the turbine
exit when the turbine stalls. The fluid rotates in a
negative direction, i.e., in the Opposite direction com-
pared to the motion of the pump. But as the turbine

Speed increases, the reduction in the fluid rate Q to-

gether with the increase of pump Speed change the direction

 

 

 

 

 

 

 

 

 

 

 

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24
of rotation of the fluid to that of the pump as shown in
Fig. 12b. The fluid also throws a positive torque on the
reaction member at high turbine Speed which tends to turn
the reaction in the direction of the pump motion. (See
Fig. 12c.)

In order to reduce the shock loss at the reaction
member entrance at high turbine speeds, the reaction mem-
ber is mounted on the converter housing with roller
clutches. As soon as the fluid begins to throw a posi-
tive torque on the reaction member, the roller clutches
allow the reaction member to rotate freely in the direc-
tion of the motion of the pump. As the reaction member
freewheels, the torque converter has a similar character-
istics of a hydraulic fluid coupling, which has high
efficiency at high turbine speed.

The efficiency of the torque converter at inter-
mediate turbine speed can be increased by dividing the
reaction member into two parts. Both parts are mounted
independently on the converter housing by roller clutches.

Both reaction members are locked to the housing
when the turbine stalls or at low turbine speed. But at
some designed point in the intermediate turbine speed
range the secondary reaction member which meets the fluid
first will start to freewheel. As the turbine runs at

high speed, the primary reaction member also start to

25
freewheel at some designed point in the direction of rota-
tion of the pump.

IMPROVEMENT OF CONVERTER PERFORMANCE BY FREEWHEELING UNITS.
The torque converter efficiency curve of a three-element
converter without freewheeling unit is shown in Fig. 13a.
The efficiency rises as the turbine Speeds up until the
designed point is reached after that point the efficiency
falls off rapidly as a result of high shock losses at
different wheels.

With a freewheeling unit as the reaction member
the efficiency curve goes up at the clutch point R, as
shown in Fig. 15b, when the reaction member starts free-
wheeling. A remarkable increase in efficiency at high
turbine speed is indicated.

The torque converter efficiency at the intermedi-
ate Speed range can be increased by using two reaction
members. The secondary and the primary reaction members
freewheel at intermediate and high turbine speeds reSpec-
tively. The efficiency curve is shown in Fig. 15c, where

RS and R are the clutch points for the secondary and

P
primary reaction members respectively. This kind of con-
verter is called four element torque converter.

'When a two piece pump takes place of the one piece

pump in the four-element torque converter, it is called a

five-element converter. In a five-element converter, the

 

 

 

 

 

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:‘avertrr converter

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the .ZxWN‘, :CMT, Five Eflsvvwrt ConVPPZOPSa

26
secondary pump is locked at a low turbine speed. The in-
crease of efficiency of the five—element converter over

that of the four-element at low turbine speed is shown in

Fig. 15d.

PART 2

TYPES OF HYDRODYNAMIC TORQUE CONVERTERS

TYPES OF HYDRODYNAMIC TORQUE CONVERTERS

The discussion of types of hydrodynamic torque con-
verters in this thesis is confined to those used in the
automobiles. Generally Speaking, all of them can be
classified as either a three or five element torque con-
verters. They produce maximum stalling torque ratios at
a little over two to one, and they are cooled either by
air or by engine cooling water with heat exchangers.

The torque converters used in the different makes
of automobiles will be discussed in the following order:
(1) Chevrolet, (2) Buick, (5) Ford and Mercury, (4)
Packard and (5) Studebaker.

TORGUE CONVERTERZIN CHEVROLET POW‘RGLIDE TRANSMISSION.
(Refer to Fig. 14) The torque converter used in the Chev-
rolet Powerglide transmission is a five-element, poly-
phase type. It consists of the following five major
elements:

1. Primary pump with 29 vanes.

2. Secondary pump with 51 vanes.

5. Turbine with 31 vanes.

4. Primary stator with 25 vanes.

5. Secondary stator with 25 vanes.

Each of these elements is a vaned wheel made from

steel stampings which are assembled in place, Spot welded

and c0pper-brazed into an integral unit.

 

Fig. 14 Longitudinal Section of the Powerglide Unit

28

The primary pump is spot-welded to the torque con-
verter housing which, in turn, is bolted to the flywheel
member. The turbine is attached to the housing cover at
the front by a special machined bolt but is permitted to
turn freely on a bronze bushing and thrust washer. The
input shaft is Splined into the flange bolted back of the
turbine hub; while to the rear of the turbine it runs through
the stator support which is the stationary part of the
transmission housing.

The secondary pump as well as the two stator mem-
bers are mounted on overrunning clutches of cam and roller
type. The clutches permit either stator to free-wheel in
the same direction as the pump and turbine but lock the
stator to the stationary stator race with the develOpment
of any forces tending to rotate it in Opposite direction.
Similarly the clutch on the secondary allows it to turn
faster, but never slower than the primary pump.

A unique feature of Powerglide is the overrunning
coupling, an auxiliary fluid coupling within the torque
converter. It consists of two vane wheels installed be-
tween the inner concave surfaces of the primary pump and
the turbine, one being attached to the pump and the other
to the turbine. The coupline element provides additional
engine braking and makes possible the extremely low speed

push start.

29

Stalling torque ratio is of the order of 2.2 to 1.
At that point both primary and secondary stators are
.fully locked by their clutches. At the same time the
secondary pump is overrunning the primary pump to reduce
shock loss. AS the torque converter picks up speed and
the demand for torque multiplication begins to lessen the
secondary pump Slows down and locks to the primary pump
hub, thus integrating both pump elements into a Single
unit giving maximum effect from now on through the fluid
coupling phase. The secondary stator then unlocks and be-
gins to free wheel. Then as engine Speed reaches the
minimum value at which engine torque alone can carry the
load, the primary stator unlocks and join the secondary
stator in free-wheeling phase. At this point the torque
converter begins to enter the fluid coupling phase.

At full throttle acceleration on a level road, the
secondary pump stops overrunning the primary at about 30
mph.

The torque converter oil is cooled by a water cooler.
TORQUE CONVERTER IN BUICK DYNAFLOW TRANSMISSION. The
torque converter used in the Buick Dynaflow transmission
is similar to Chevrolet converter in appearance except
the omission of the overrunning coupling. It consists of
five elements: primary and secondary pump, turbine, pri-
mary and secondary reaction members. All of them are made

from die-cast aluminum alloy.

50

The primary pump is driven from the engine shaft
through a flexible disk, which takes the place of a fly-
wheel. This flexible disk reduces the mechanical vibra-
-tion transfer from the engine to the transmission and
also lessens the harmful effect due to misalignment of
the engine and the transmission shafts.

Before the fluid reaches the primary pump it
passes through a secondary pump, which is supported on
the hub of the primary pump through a roller clutch.

From the primary pump the fluid passes into the turbine,
in which it flows toward the axis of rotation. The tur-
bine discharges the fluid into the two part reaction
member. Both are mounted on roller clutches, of which

the stationary ring of race is secured to the transmission
housing. These clutches allow the reaction members to
turn freely in the direction of pump rotation whenever

the direction of flow at their entrances tends to turn
them in that direction, but prevent them from turning in
the Opposite direction.

The maximum stalling torque ratio is 2.25 to 1
when both primary and secondary reaction members are
locked by their clutches, and when the secondary pump is
freewheeling ahead of the primary pump. As the torque
converter picks up speed, the secondary pump is locked to

the primary pump hub, and both pumps become an integral

51
unit. Then as the torque converter Speeds up further,
the secondary reaction member starts to freewheel.
Finally the primary reaction member freewheels as soon
as the engine torque alone can carry the load.

At full throttle acceleration on a level road, the
secondary pump stops overrunning the primary pump at about
57 mph. The torque converter is oil cooled by using an
heat exchanger.

TORQUE CONVERTER LN MERCURY-FORD TRANSMISSION. (Refer

to Fig. 15.) The torque converter used in the Mercury-
Ford transmission is composed of three elements: pump
turbine and stator (reaction member). It is driven from
the engine through a flexible plate for minimum vibra-
tion transfer from the engine to the transmission. Fins
cast on the pump cover provide added cooling surface and
serve as vanes for pumping air. Air for cooling is drawn
in at the lower left side, passes through the converter
housing by centrifugal action, and is exhausted at the
lower right Side. This method of cooling the converter
and transmission oil eliminates the need for plumbing and
is said to be completely effective under all operating
conditions.

Slots are provided in the inside of the die cast
pump cover to locate 31 stamped steel blades, each of

which is held in place by four tabs while a retaining

 

O
-—_—_

, ~ ' O O C I
, , nIHIIIIHHIIIIIIHIIHI

Fig. 15 Longitudinal Section of the Ford-Mercury
Automatic Transmission

32
ring assists in holding all of the blades. An addi-
tional pair of tabs on each blade project through slots
in the torus ring and are rolled over, this holding the
torus ring in place. The pump cover is fastened to a
cast iron hub by cab screws, and sealed with a synthetic
ring to prevent leakage at the joint.

Except for a forged steel hub, the turbine is made
of steel stampings. Four tabs extending from each of the
53 blades through the outer Shell are bent over to hold
the blades in place. Two additional tabs on each blade
hold the torus ring in place in the same manner as in the
pump assembly. The outer Shell is fastened to the Splined
steel hub by rivets.

The stator is an aluminum die casting to which a
formed, split steel Shroud is assembled and held in place
by welding at the Split. Splines on the outer race of the
Sprag type overrunning clutch prevent rotation in the
stator hub, and snap rings in conjunction with two sup-
ports hold the race in place.

The maximum stalling torque ratio is in the order
of 2.1 to l.

TORQUE CONVERTER IN PACKARD ULTRAMATIC TRANSMISSION. The
torque converter as Shown in Fig. 16 in Packard Ultra-
matic transmission appears to be a four element torque

converter. Actually it is a three-element type with two

 

 

Fig. 16

s 0

 

Packard Automatic Transmission

SECTION A-A

. 33
turbines bolted together. The first turbine is nearest to
the engine end and has been bolted to it the smaller
diameter second turbine stage which is seen at the rear
end of the torque converter. Being bolted together they
act as a unit.

The pump, which also serves as the housing for the
assembly, is at the rear and is carried forward to bolt
to the flexible disk on the crankshaft. The latter re-
places the conventional flywheel, since the entire mass
of the converter is now a part of the flywheel system.
The disk also serves to provide the flexibility required
in a complicated system of this nature, making up for any
tendency to misalignment at any time.

The reaction member is between the first and
second turbine stages and is mounted on a sleeve which
terminates at the bulkhead with a one-way clutch of Sprag
type. The overrunning clutch serves to lock the reaction
member during the phase of torque multiplication, then
releases it when the coupling point is reached. The con-
verter then acts as a coupling until the direct clutch
engages. Consequently, the reaction member is free to
rotate at.all times except when torque multiplication is
required.

The first and second turbine elements are made with

formed blades having a rounded nose and sharp exit. The

34
pump blades, too, have a round nose and sharp exit but in-
corporate a constant section for the major portion of the
length of the blade measuring from the nose. The second
turbine element is so formed and positioned as to control
the flow into the pump to achieve a rising input speed
curve, starting with an engine speed of around 1600 rpm.
At the same time it has the effect of extending the clutch
point for smooth engagement. Through the action of modu-
lator valving the torque converter contains an oil pressure
of about 30 psi.

Although the converter is a three element type with
but one reactor stage for torque multiplication, yet it
is able to attain a stalling torque ratio in the order of
2.4 to l.

The converter, as well as those used in the Chev-
rolet Powerglide and Buick Dynaflow transmissions, is
cooled by a water-cooled oil cooler.

TORQUE CONVERTER IN STUDEBAKER TURBOMATIC TRANSMISSION.
The torque converter used in the Studebaker Turbomatic
transmission, as Shown in Fig. 17, is of the three ele-
ment type having the pump member connected to the crank-
shaft. The turbine member, at the left, connected to the
output shaft; and the stator member, for torque multi-
plication and reverse of fluid flow, at the center. The

latter is mounted on a Sprag type free-wheel unit

. .2- .88 :89 £32.01 9.: .23. .02.. 3 u u o a o 2:.
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\ \\ 9
d 3" . t V . 1 .\
\ \ . \\ . \\ RSV». .\\o\ \ 9 ' 0' x \
\ y. \ .vo 9 if. .. x ‘ \xfl \. L --
. .\ ‘\ . . \\ .‘x \ . \ .\ \ \ u
u s \ \ \ . . v
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55
connected to the case to permit only one direction of
rotation. Maximum torque multiplication, at stall, is
of the order of 2.15 to one and this occurs at an engine
Speed of 15 rpm.

The torque converter is made up of fabricated ele-
ments and does not employ castings for the wheels. In
essence it is an assembly of stamped pieces with indi-
vidual stampings for the vanes of the three elements.

The torque converter is air-cooled. This is
effected by attaching a formed sheet metal Shell or baffle
fitted with eight vanes to serve as a centrifugal pump,
thus giving the air stream positive direction and forcing

it to scrub the surface of the torque converter.

‘BIBLIOGRAPHY

Eksergian, Rupen, "On the Reaction of Fluids and Fluid
Jets”, Franklin Institute Journal, Vol. 257, No. 5,
pp. 585-410, (May, 1944).

Eksergian, Rupen, ”The Torque Converter and Fluid Coupling",
Franklin institute Journal, Vol. 255, No. 5. pp. 441-
478, May, 1943).

Heldt, P. M., Torque Converters, P. M. Heldt, Nyack, N. Y.,
1947.

Kelly, 0. K., "How the Torque Converter Works", SAE Jour-
nal, Vol. 57, No. 2, pp. 22-25, (Feb., 1949).

Kelly, 0. K., ”Making Torque Converters More Efficient",
SAE Journal, Vol. 57, No. 4, pp. 20-25, (April, 1949).

Modern Automatic Transmission, Chilton Company, Phila-
delphia, Penna., 1950.

Rouse, Hunter, Elementary Mechanics g: Fluids, John Wiley
& Sons, N. Y., 1945.

Spannhake, E. W., "Hydrodynamics of the Hydraulic Fluid
Coupling", SAE Journal, Vol. 57, No. 8, pp. 59-66,
(August, 1949).

MICHIGRN STQTE UNIV. LIBRQRIES

J

l {M H) H III! II WI

1.
1
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